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/Nim

std/macros

This module contains the interface to the compiler's abstract syntax tree (AST). Macros operate on this tree.

The AST in Nim

This section describes how the AST is modelled with Nim's type system. The AST consists of nodes (NimNode) with a variable number of children. Each node has a field named kind which describes what the node contains:

type
  NimNodeKind = enum     ## kind of a node; only explanatory
    nnkNone,             ## invalid node kind
    nnkEmpty,            ## empty node
    nnkIdent,            ## node contains an identifier
    nnkIntLit,           ## node contains an int literal (example: 10)
    nnkStrLit,           ## node contains a string literal (example: "abc")
    nnkNilLit,           ## node contains a nil literal (example: nil)
    nnkCaseStmt,         ## node represents a case statement
    ...                  ## many more
  
  NimNode = ref NimNodeObj
  NimNodeObj = object
    case kind: NimNodeKind           ## the node's kind
    of nnkNone, nnkEmpty, nnkNilLit:
      discard                        ## node contains no additional fields
    of nnkCharLit..nnkUInt64Lit:
      intVal: BiggestInt             ## the int literal
    of nnkFloatLit..nnkFloat64Lit:
      floatVal: BiggestFloat         ## the float literal
    of nnkStrLit..nnkTripleStrLit, nnkCommentStmt, nnkIdent, nnkSym:
      strVal: string                 ## the string literal
    else:
      sons: seq[NimNode]             ## the node's sons (or children)

For the NimNode type, the [] operator has been overloaded: n[i] is n's i-th child.

To specify the AST for the different Nim constructs, the notation nodekind(son1, son2, ...) or nodekind(value) or nodekind(field=value) is used.

Some child may be missing. A missing child is a node of kind nnkEmpty; a child can never be nil.

Leaf nodes/Atoms

A leaf of the AST often corresponds to a terminal symbol in the concrete syntax. Note that the default float in Nim maps to float64 such that the default AST for a float is nnkFloat64Lit as below.

Nim expression	Corresponding AST
`42`	`nnkIntLit(intVal = 42)`
`42'i8`	`nnkInt8Lit(intVal = 42)`
`42'i16`	`nnkInt16Lit(intVal = 42)`
`42'i32`	`nnkInt32Lit(intVal = 42)`
`42'i64`	`nnkInt64Lit(intVal = 42)`
`42'u8`	`nnkUInt8Lit(intVal = 42)`
`42'u16`	`nnkUInt16Lit(intVal = 42)`
`42'u32`	`nnkUInt32Lit(intVal = 42)`
`42'u64`	`nnkUInt64Lit(intVal = 42)`
`42.0`	`nnkFloat64Lit(floatVal = 42.0)`
`42.0'f32`	`nnkFloat32Lit(floatVal = 42.0)`
`42.0'f64`	`nnkFloat64Lit(floatVal = 42.0)`
`"abc"`	`nnkStrLit(strVal = "abc")`
`r"abc"`	`nnkRStrLit(strVal = "abc")`
`"""abc"""`	`nnkTripleStrLit(strVal = "abc")`
`' '`	`nnkCharLit(intVal = 32)`
`nil`	`nnkNilLit()`
`myIdentifier`	`nnkIdent(strVal = "myIdentifier")`
`myIdentifier`	after lookup pass: `nnkSym(strVal = "myIdentifier", ...)`

Identifiers are nnkIdent nodes. After the name lookup pass these nodes get transferred into nnkSym nodes.

Calls/expressions

Command call

Concrete syntax:

echo "abc", "xyz"

AST:

nnkCommand(
  nnkIdent("echo"),
  nnkStrLit("abc"),
  nnkStrLit("xyz")
)

Call with `()`

Concrete syntax:

echo("abc", "xyz")

AST:

nnkCall(
  nnkIdent("echo"),
  nnkStrLit("abc"),
  nnkStrLit("xyz")
)

Infix operator call

Concrete syntax:

"abc" & "xyz"

AST:

nnkInfix(
  nnkIdent("&"),
  nnkStrLit("abc"),
  nnkStrLit("xyz")
)

Note that with multiple infix operators, the command is parsed by operator precedence.

Concrete syntax:

5 + 3 * 4

AST:

nnkInfix(
  nnkIdent("+"),
  nnkIntLit(5),
  nnkInfix(
    nnkIdent("*"),
    nnkIntLit(3),
    nnkIntLit(4)
  )
)

As a side note, if you choose to use infix operators in a prefix form, the AST behaves as a parenthetical function call with nnkAccQuoted, as follows:

Concrete syntax:

`+`(3, 4)

AST:

nnkCall(
  nnkAccQuoted(
    nnkIdent("+")
  ),
  nnkIntLit(3),
  nnkIntLit(4)
)

Prefix operator call

Concrete syntax:

? "xyz"

AST:

nnkPrefix(
  nnkIdent("?"),
  nnkStrLit("abc")
)

Postfix operator call

Note: There are no postfix operators in Nim. However, the nnkPostfix node is used for the asterisk export marker *:

Concrete syntax:

identifier*

AST:

nnkPostfix(
  nnkIdent("*"),
  nnkIdent("identifier")
)

Call with named arguments

Concrete syntax:

writeLine(file=stdout, "hallo")

AST:

nnkCall(
  nnkIdent("writeLine"),
  nnkExprEqExpr(
    nnkIdent("file"),
    nnkIdent("stdout")
  ),
  nnkStrLit("hallo")
)

Call with raw string literal

This is used, for example, in the bindSym examples here and with re"some regexp" in the regular expression module.

Concrete syntax:

echo"abc"

AST:

nnkCallStrLit(
  nnkIdent("echo"),
  nnkRStrLit("hello")
)

Dereference operator `[]`

Concrete syntax:

x[]

AST:

nnkDerefExpr(nnkIdent("x"))

Addr operator

Concrete syntax:

addr(x)

AST:

nnkAddr(nnkIdent("x"))

Cast operator

Concrete syntax:

cast[T](x)

AST:

nnkCast(nnkIdent("T"), nnkIdent("x"))

Object access operator `.`

Concrete syntax:

x.y

AST:

nnkDotExpr(nnkIdent("x"), nnkIdent("y"))

If you use Nim's flexible calling syntax (as in x.len()), the result is the same as above but wrapped in an nnkCall.

Array access operator `[]`

Concrete syntax:

x[y]

AST:

nnkBracketExpr(nnkIdent("x"), nnkIdent("y"))

Parentheses

Parentheses for affecting operator precedence use the nnkPar node.

Concrete syntax:

(a + b) * c

AST:

nnkInfix(nnkIdent("*"),
  nnkPar(
    nnkInfix(nnkIdent("+"), nnkIdent("a"), nnkIdent("b"))),
  nnkIdent("c"))

Tuple Constructors

Nodes for tuple construction are built with the nnkTupleConstr node.

Concrete syntax:

(1, 2, 3)
(a: 1, b: 2, c: 3)
()

AST:

nnkTupleConstr(nnkIntLit(1), nnkIntLit(2), nnkIntLit(3))
nnkTupleConstr(
  nnkExprColonExpr(nnkIdent("a"), nnkIntLit(1)),
  nnkExprColonExpr(nnkIdent("b"), nnkIntLit(2)),
  nnkExprColonExpr(nnkIdent("c"), nnkIntLit(3)))
nnkTupleConstr()

Since the one tuple would be syntactically identical to parentheses with an expression in them, the parser expects a trailing comma for them. For tuple constructors with field names, this is not necessary.

(1,)
(a: 1)

AST:

nnkTupleConstr(nnkIntLit(1))
nnkTupleConstr(
  nnkExprColonExpr(nnkIdent("a"), nnkIntLit(1)))

Curly braces

Curly braces are used as the set constructor.

Concrete syntax:

{1, 2, 3}

AST:

nnkCurly(nnkIntLit(1), nnkIntLit(2), nnkIntLit(3))

When used as a table constructor, the syntax is different.

Concrete syntax:

{a: 3, b: 5}

AST:

nnkTableConstr(
  nnkExprColonExpr(nnkIdent("a"), nnkIntLit(3)),
  nnkExprColonExpr(nnkIdent("b"), nnkIntLit(5))
)

Brackets

Brackets are used as the array constructor.

Concrete syntax:

[1, 2, 3]

AST:

nnkBracket(nnkIntLit(1), nnkIntLit(2), nnkIntLit(3))

Ranges

Ranges occur in set constructors, case statement branches, or array slices. Internally, the node kind nnkRange is used, but when constructing the AST, construction with .. as an infix operator should be used instead.

Concrete syntax:

1..3

AST:

nnkInfix(
  nnkIdent(".."),
  nnkIntLit(1),
  nnkIntLit(3)
)

Example code:

macro genRepeatEcho() =
  result = newNimNode(nnkStmtList)
  
  var forStmt = newNimNode(nnkForStmt) # generate a for statement
  forStmt.add(ident("i")) # use the variable `i` for iteration
  
  var rangeDef = newNimNode(nnkInfix).add(
    ident("..")).add(
    newIntLitNode(3),newIntLitNode(5)) # iterate over the range 3..5
  
  forStmt.add(rangeDef)
  forStmt.add(newCall(ident("echo"), newIntLitNode(3))) # meat of the loop
  result.add(forStmt)

genRepeatEcho() # gives:
                # 3
                # 3
                # 3

If expression

The representation of the if expression is subtle, but easy to traverse.

Concrete syntax:

if cond1: expr1 elif cond2: expr2 else: expr3

AST:

nnkIfExpr(
  nnkElifExpr(cond1, expr1),
  nnkElifExpr(cond2, expr2),
  nnkElseExpr(expr3)
)

Documentation Comments

Double-hash (##) comments in the code actually have their own format, using strVal to get and set the comment text. Single-hash (#) comments are ignored.

Concrete syntax:

## This is a comment
## This is part of the first comment
stmt1
## Yet another

AST:

nnkCommentStmt() # only appears once for the first two lines!
stmt1
nnkCommentStmt() # another nnkCommentStmt because there is another comment
                 # (separate from the first)

Pragmas

One of Nim's cool features is pragmas, which allow fine-tuning of various aspects of the language. They come in all types, such as adorning procs and objects, but the standalone emit pragma shows the basics with the AST.

Concrete syntax:

{.emit: "#include <stdio.h>".}

AST:

nnkPragma(
  nnkExprColonExpr(
    nnkIdent("emit"),
    nnkStrLit("#include <stdio.h>") # the "argument"
  )
)

As many nnkIdent appear as there are pragmas between {..}. Note that the declaration of new pragmas is essentially the same:

Concrete syntax:

{.pragma: cdeclRename, cdecl.}

AST:

nnkPragma(
  nnkExprColonExpr(
    nnkIdent("pragma"), # this is always first when declaring a new pragma
    nnkIdent("cdeclRename") # the name of the pragma
  ),
  nnkIdent("cdecl")
)

Statements

If statement

The representation of the if statement is subtle, but easy to traverse. If there is no else branch, no nnkElse child exists.

Concrete syntax:

if cond1:
  stmt1
elif cond2:
  stmt2
elif cond3:
  stmt3
else:
  stmt4

AST:

nnkIfStmt(
  nnkElifBranch(cond1, stmt1),
  nnkElifBranch(cond2, stmt2),
  nnkElifBranch(cond3, stmt3),
  nnkElse(stmt4)
)

When statement

Like the if statement, but the root has the kind nnkWhenStmt.

Assignment

Concrete syntax:

x = 42

AST:

nnkAsgn(nnkIdent("x"), nnkIntLit(42))

This is not the syntax for assignment when combined with var, let, or const.

Statement list

Concrete syntax:

stmt1
stmt2
stmt3

AST:

nnkStmtList(stmt1, stmt2, stmt3)

Case statement

Concrete syntax:

case expr1
of expr2, expr3..expr4:
  stmt1
of expr5:
  stmt2
elif cond1:
  stmt3
else:
  stmt4

AST:

nnkCaseStmt(
  expr1,
  nnkOfBranch(expr2, nnkRange(expr3, expr4), stmt1),
  nnkOfBranch(expr5, stmt2),
  nnkElifBranch(cond1, stmt3),
  nnkElse(stmt4)
)

The nnkElifBranch and nnkElse parts may be missing.

While statement

Concrete syntax:

while expr1:
  stmt1

AST:

nnkWhileStmt(expr1, stmt1)

For statement

Concrete syntax:

for ident1, ident2 in expr1:
  stmt1

AST:

nnkForStmt(ident1, ident2, expr1, stmt1)

Try statement

Concrete syntax:

try:
  stmt1
except e1, e2:
  stmt2
except e3:
  stmt3
except:
  stmt4
finally:
  stmt5

AST:

nnkTryStmt(
  stmt1,
  nnkExceptBranch(e1, e2, stmt2),
  nnkExceptBranch(e3, stmt3),
  nnkExceptBranch(stmt4),
  nnkFinally(stmt5)
)

Return statement

Concrete syntax:

return expr1

AST:

nnkReturnStmt(expr1)

Yield statement

Like return, but with nnkYieldStmt kind.

nnkYieldStmt(expr1)

Discard statement

Like return, but with nnkDiscardStmt kind.

nnkDiscardStmt(expr1)

Continue statement

Concrete syntax:

continue

AST:

nnkContinueStmt()

Break statement

Concrete syntax:

break otherLocation

AST:

nnkBreakStmt(nnkIdent("otherLocation"))

If break is used without a jump-to location, nnkEmpty replaces nnkIdent.

Block statement

Concrete syntax:

block name:

AST:

nnkBlockStmt(nnkIdent("name"), nnkStmtList(...))

A block doesn't need an name, in which case nnkEmpty is used.

Asm statement

Concrete syntax:

asm """
  some asm
"""

AST:

nnkAsmStmt(
  nnkEmpty(), # for pragmas
  nnkTripleStrLit("some asm"),
)

Import section

Nim's import statement actually takes different variations depending on what keywords are present. Let's start with the simplest form.

Concrete syntax:

import std/math

AST:

nnkImportStmt(nnkIdent("math"))

With except, we get nnkImportExceptStmt.

Concrete syntax:

import std/math except pow

AST:

nnkImportExceptStmt(nnkIdent("math"),nnkIdent("pow"))

Note that import std/math as m does not use a different node; rather, we use nnkImportStmt with as as an infix operator.

Concrete syntax:

import std/strutils as su

AST:

nnkImportStmt(
  nnkInfix(
    nnkIdent("as"),
    nnkIdent("strutils"),
    nnkIdent("su")
  )
)

From statement

If we use from ... import, the result is different, too.

Concrete syntax:

from std/math import pow

AST:

nnkFromStmt(nnkIdent("math"), nnkIdent("pow"))

Using from std/math as m import pow works identically to the as modifier with the import statement, but wrapped in nnkFromStmt.

Export statement

When you are making an imported module accessible by modules that import yours, the export syntax is pretty straightforward.

Concrete syntax:

export unsigned

AST:

nnkExportStmt(nnkIdent("unsigned"))

Similar to the import statement, the AST is different for export ... except.

Concrete syntax:

export math except pow # we're going to implement our own exponentiation

AST:

nnkExportExceptStmt(nnkIdent("math"),nnkIdent("pow"))

Include statement

Like a plain import statement but with nnkIncludeStmt.

Concrete syntax:

include blocks

AST:

nnkIncludeStmt(nnkIdent("blocks"))

Var section

Concrete syntax:

var a = 3

AST:

nnkVarSection(
  nnkIdentDefs(
    nnkIdent("a"),
    nnkEmpty(), # or nnkIdent(...) if the variable declares the type
    nnkIntLit(3),
  )
)

Note that either the second or third (or both) parameters above must exist, as the compiler needs to know the type somehow (which it can infer from the given assignment).

This is not the same AST for all uses of var. See Procedure declaration for details.

Let section

This is equivalent to var, but with nnkLetSection rather than nnkVarSection.

Concrete syntax:

let a = 3

AST:

nnkLetSection(
  nnkIdentDefs(
    nnkIdent("a"),
    nnkEmpty(), # or nnkIdent(...) for the type
    nnkIntLit(3),
  )
)

Const section

Concrete syntax:

const a = 3

AST:

nnkConstSection(
  nnkConstDef( # not nnkConstDefs!
    nnkIdent("a"),
    nnkEmpty(), # or nnkIdent(...) if the variable declares the type
    nnkIntLit(3), # required in a const declaration!
  )
)

Type section

Starting with the simplest case, a type section appears much like var and const.

Concrete syntax:

type A = int

AST:

nnkTypeSection(
  nnkTypeDef(
    nnkIdent("A"),
    nnkEmpty(),
    nnkIdent("int")
  )
)

Declaring distinct types is similar, with the last nnkIdent wrapped in nnkDistinctTy.

Concrete syntax:

type MyInt = distinct int

AST:

# ...
nnkTypeDef(
  nnkIdent("MyInt"),
  nnkEmpty(),
  nnkDistinctTy(
    nnkIdent("int")
  )
)

If a type section uses generic parameters, they are treated here:

Concrete syntax:

type A[T] = expr1

AST:

nnkTypeSection(
  nnkTypeDef(
    nnkIdent("A"),
    nnkGenericParams(
      nnkIdentDefs(
        nnkIdent("T"),
        nnkEmpty(), # if the type is declared with options, like
                    # ``[T: SomeInteger]``, they are given here
        nnkEmpty(),
      )
    )
    expr1,
  )
)

Note that not all nnkTypeDef utilize nnkIdent as their parameter. One of the most common uses of type declarations is to work with objects.

Concrete syntax:

type IO = object of RootObj

AST:

# ...
nnkTypeDef(
  nnkIdent("IO"),
  nnkEmpty(),
  nnkObjectTy(
    nnkEmpty(), # no pragmas here
    nnkOfInherit(
      nnkIdent("RootObj") # inherits from RootObj
    ),
    nnkEmpty()
  )
)

Nim's object syntax is rich. Let's take a look at an involved example in its entirety to see some of the complexities.

Concrete syntax:

type Obj[T] {.inheritable.} = object
  name: string
  case isFat: bool
  of true:
    m: array[100_000, T]
  of false:
    m: array[10, T]

AST:

# ...
nnkPragmaExpr(
  nnkIdent("Obj"),
  nnkPragma(nnkIdent("inheritable"))
),
nnkGenericParams(
nnkIdentDefs(
  nnkIdent("T"),
  nnkEmpty(),
  nnkEmpty())
),
nnkObjectTy(
  nnkEmpty(),
  nnkEmpty(),
  nnkRecList( # list of object parameters
    nnkIdentDefs(
      nnkIdent("name"),
      nnkIdent("string"),
      nnkEmpty()
    ),
    nnkRecCase( # case statement within object (not nnkCaseStmt)
      nnkIdentDefs(
        nnkIdent("isFat"),
        nnkIdent("bool"),
        nnkEmpty()
      ),
      nnkOfBranch(
        nnkIdent("true"),
        nnkRecList( # again, a list of object parameters
          nnkIdentDefs(
            nnkIdent("m"),
            nnkBracketExpr(
              nnkIdent("array"),
              nnkIntLit(100000),
              nnkIdent("T")
            ),
            nnkEmpty()
        )
      ),
      nnkOfBranch(
        nnkIdent("false"),
        nnkRecList(
          nnkIdentDefs(
            nnkIdent("m"),
            nnkBracketExpr(
              nnkIdent("array"),
              nnkIntLit(10),
              nnkIdent("T")
            ),
            nnkEmpty()
          )
        )
      )
    )
  )
)

Using an enum is similar to using an object.

Concrete syntax:

type X = enum
  First

AST:

# ...
nnkEnumTy(
  nnkEmpty(),
  nnkIdent("First") # you need at least one nnkIdent or the compiler complains
)

The usage of concept (experimental) is similar to objects.

Concrete syntax:

type Con = concept x,y,z
  (x & y & z) is string

AST:

# ...
nnkTypeClassTy( # note this isn't nnkConceptTy!
  nnkArgList(
    # ... idents for x, y, z
  )
  # ...
)

Static types, like static[int], use nnkIdent wrapped in nnkStaticTy.

Concrete syntax:

type A[T: static[int]] = object

AST:

# ... within nnkGenericParams
nnkIdentDefs(
  nnkIdent("T"),
  nnkStaticTy(
    nnkIdent("int")
  ),
  nnkEmpty()
)
# ...

In general, declaring types mirrors this syntax (i.e., nnkStaticTy for static, etc.). Examples follow (exceptions marked by *):

Nim type	Corresponding AST
`static`	`nnkStaticTy`
`tuple`	`nnkTupleTy`
`var`	`nnkVarTy`
`ptr`	`nnkPtrTy`
`ref`	`nnkRefTy`
`distinct`	`nnkDistinctTy`
`enum`	`nnkEnumTy`
`concept`	`nnkTypeClassTy`*
`array`	`nnkBracketExpr(nnkIdent("array"),...`*
`proc`	`nnkProcTy`
`iterator`	`nnkIteratorTy`
`object`	`nnkObjectTy`

Take special care when declaring types as proc. The behavior is similar to Procedure declaration, below, but does not treat nnkGenericParams. Generic parameters are treated in the type, not the proc itself.

Concrete syntax:

type MyProc[T] = proc(x: T) {.nimcall.}

AST:

# ...
nnkTypeDef(
  nnkIdent("MyProc"),
  nnkGenericParams( # here, not with the proc
    # ...
  )
  nnkProcTy( # behaves like a procedure declaration from here on
    nnkFormalParams(
      # ...
    ),
    nnkPragma(nnkIdent("nimcall"))
  )
)

The same syntax applies to iterator (with nnkIteratorTy), but does not apply to converter or template.

Type class versions of these nodes generally share the same node kind but without any child nodes. The tuple type class is represented by nnkTupleClassTy, while a proc or iterator type class with pragmas has an nnkEmpty node in place of the nnkFormalParams node of a concrete proc or iterator type node.

type TypeClass = proc {.nimcall.} | ref | tuple

AST:

nnkTypeDef(
  nnkIdent("TypeClass"),
  nnkEmpty(),
  nnkInfix(
    nnkIdent("|"),
    nnkProcTy(
      nnkEmpty(),
      nnkPragma(nnkIdent("nimcall"))
    ),
    nnkInfix(
      nnkIdent("|"),
      nnkRefTy(),
      nnkTupleClassTy()
    )
  )
)

Mixin statement

Concrete syntax:

mixin x

AST:

nnkMixinStmt(nnkIdent("x"))

Bind statement

Concrete syntax:

bind x

AST:

nnkBindStmt(nnkIdent("x"))

Procedure declaration

Let's take a look at a procedure with a lot of interesting aspects to get a feel for how procedure calls are broken down.

Concrete syntax:

proc hello*[T: SomeInteger](x: int = 3, y: float32): int {.inline.} = discard

AST:

nnkProcDef(
  nnkPostfix(nnkIdent("*"), nnkIdent("hello")), # the exported proc name
  nnkEmpty(), # patterns for term rewriting in templates and macros (not procs)
  nnkGenericParams( # generic type parameters, like with type declaration
    nnkIdentDefs(
      nnkIdent("T"),
      nnkIdent("SomeInteger"),
      nnkEmpty()
    )
  ),
  nnkFormalParams(
    nnkIdent("int"), # the first FormalParam is the return type. nnkEmpty() if there is none
    nnkIdentDefs(
      nnkIdent("x"),
      nnkIdent("int"), # type type (required for procs, not for templates)
      nnkIntLit(3) # a default value
    ),
    nnkIdentDefs(
      nnkIdent("y"),
      nnkIdent("float32"),
      nnkEmpty()
    )
  ),
  nnkPragma(nnkIdent("inline")),
  nnkEmpty(), # reserved slot for future use
  nnkStmtList(nnkDiscardStmt(nnkEmpty())) # the meat of the proc
)

There is another consideration. Nim has flexible type identification for its procs. Even though proc(a: int, b: int) and proc(a, b: int) are equivalent in the code, the AST is a little different for the latter.

Concrete syntax:

proc(a, b: int)

AST:

# ...AST as above...
nnkFormalParams(
  nnkEmpty(), # no return here
  nnkIdentDefs(
    nnkIdent("a"), # the first parameter
    nnkIdent("b"), # directly to the second parameter
    nnkIdent("int"), # their shared type identifier
    nnkEmpty(), # default value would go here
  )
),
# ...

When a procedure uses the special var type return variable, the result is different from that of a var section.

Concrete syntax:

proc hello(): var int

AST:

# ...
nnkFormalParams(
  nnkVarTy(
    nnkIdent("int")
  )
)

Iterator declaration

The syntax for iterators is similar to procs, but with nnkIteratorDef replacing nnkProcDef.

Concrete syntax:

iterator nonsense[T](x: seq[T]): float {.closure.} = ...

AST:

nnkIteratorDef(
  nnkIdent("nonsense"),
  nnkEmpty(),
  ...
)

Converter declaration

A converter is similar to a proc.

Concrete syntax:

converter toBool(x: float): bool

AST:

nnkConverterDef(
  nnkIdent("toBool"),
  # ...
)

Template declaration

Templates (as well as macros, as we'll see) have a slightly expanded AST when compared to procs and iterators. The reason for this is term-rewriting macros. Notice the nnkEmpty() as the second argument to nnkProcDef and nnkIteratorDef above? That's where the term-rewriting macros go.

Concrete syntax:

template optOpt{expr1}(a: int): int

AST:

nnkTemplateDef(
  nnkIdent("optOpt"),
  nnkStmtList( # instead of nnkEmpty()
    expr1
  ),
  # follows like a proc or iterator
)

If the template does not have types for its parameters, the type identifiers inside nnkFormalParams just becomes nnkEmpty.

Macro declaration

Macros behave like templates, but nnkTemplateDef is replaced with nnkMacroDef.

Hidden Standard Conversion

var f: float = 1

The type of "f" is float but the type of "1" is actually int. Inserting int into a float is a type error. Nim inserts the nnkHiddenStdConv node around the nnkIntLit node so that the new node has the correct type of float. This works for any auto converted nodes and makes the conversion explicit.

Special node kinds

There are several node kinds that are used for semantic checking or code generation. These are accessible from this module, but should not be used. Other node kinds are especially designed to make AST manipulations easier. These are explained here.

To be written.

Imports

since

Types

BindSymRule = enum brClosed, ## only the symbols in current scope are bound brOpen, ## open for overloaded symbols, but may be a single ## symbol if not ambiguous (the rules match that of ## binding in generics) brForceOpen ## same as brOpen, but it will always be open even ## if not ambiguous (this cannot be achieved with ## any other means in the language currently): Specifies how bindSym behaves. The difference between open and closed symbols can be found in manual.html#symbol-lookup-in-generics-open-and-closed-symbols Source Edit
LineInfo = object filename*: string line*, column*: int: Source Edit
NimIdent {....deprecated.} = object of RootObj: Deprecated
Represents a Nim identifier in the AST. Note: This is only rarely useful, for identifier construction from a string use ident"abc". Source Edit
NimNodeKind = enum nnkNone, nnkEmpty, nnkIdent, nnkSym, nnkType, nnkCharLit, nnkIntLit, nnkInt8Lit, nnkInt16Lit, nnkInt32Lit, nnkInt64Lit, nnkUIntLit, nnkUInt8Lit, nnkUInt16Lit, nnkUInt32Lit, nnkUInt64Lit, nnkFloatLit, nnkFloat32Lit, nnkFloat64Lit, nnkFloat128Lit, nnkStrLit, nnkRStrLit, nnkTripleStrLit, nnkNilLit, nnkComesFrom, nnkDotCall, nnkCommand, nnkCall, nnkCallStrLit, nnkInfix, nnkPrefix, nnkPostfix, nnkHiddenCallConv, nnkExprEqExpr, nnkExprColonExpr, nnkIdentDefs, nnkVarTuple, nnkPar, nnkObjConstr, nnkCurly, nnkCurlyExpr, nnkBracket, nnkBracketExpr, nnkPragmaExpr, nnkRange, nnkDotExpr, nnkCheckedFieldExpr, nnkDerefExpr, nnkIfExpr, nnkElifExpr, nnkElseExpr, nnkLambda, nnkDo, nnkAccQuoted, nnkTableConstr, nnkBind, nnkClosedSymChoice, nnkOpenSymChoice, nnkHiddenStdConv, nnkHiddenSubConv, nnkConv, nnkCast, nnkStaticExpr, nnkAddr, nnkHiddenAddr, nnkHiddenDeref, nnkObjDownConv, nnkObjUpConv, nnkChckRangeF, nnkChckRange64, nnkChckRange, nnkStringToCString, nnkCStringToString, nnkAsgn, nnkFastAsgn, nnkGenericParams, nnkFormalParams, nnkOfInherit, nnkImportAs, nnkProcDef, nnkMethodDef, nnkConverterDef, nnkMacroDef, nnkTemplateDef, nnkIteratorDef, nnkOfBranch, nnkElifBranch, nnkExceptBranch, nnkElse, nnkAsmStmt, nnkPragma, nnkPragmaBlock, nnkIfStmt, nnkWhenStmt, nnkForStmt, nnkParForStmt, nnkWhileStmt, nnkCaseStmt, nnkTypeSection, nnkVarSection, nnkLetSection, nnkConstSection, nnkConstDef, nnkTypeDef, nnkYieldStmt, nnkDefer, nnkTryStmt, nnkFinally, nnkRaiseStmt, nnkReturnStmt, nnkBreakStmt, nnkContinueStmt, nnkBlockStmt, nnkStaticStmt, nnkDiscardStmt, nnkStmtList, nnkImportStmt, nnkImportExceptStmt, nnkExportStmt, nnkExportExceptStmt, nnkFromStmt, nnkIncludeStmt, nnkBindStmt, nnkMixinStmt, nnkUsingStmt, nnkCommentStmt, nnkStmtListExpr, nnkBlockExpr, nnkStmtListType, nnkBlockType, nnkWith, nnkWithout, nnkTypeOfExpr, nnkObjectTy, nnkTupleTy, nnkTupleClassTy, nnkTypeClassTy, nnkStaticTy, nnkRecList, nnkRecCase, nnkRecWhen, nnkRefTy, nnkPtrTy, nnkVarTy, nnkConstTy, nnkOutTy, nnkDistinctTy, nnkProcTy, nnkIteratorTy, nnkSinkAsgn, nnkEnumTy, nnkEnumFieldDef, nnkArgList, nnkPattern, nnkHiddenTryStmt, nnkClosure, nnkGotoState, nnkState, nnkBreakState, nnkFuncDef, nnkTupleConstr, nnkError, ## erroneous AST node nnkModuleRef, nnkReplayAction, nnkNilRodNode, ## internal IC nodes nnkOpenSym: Source Edit
NimNodeKinds = set[NimNodeKind]: Source Edit
NimSym {....deprecated.} = ref NimSymObj: Deprecated
Represents a Nim symbol in the compiler; a symbol is a looked-up ident. Source Edit
NimSymKind = enum nskUnknown, nskConditional, nskDynLib, nskParam, nskGenericParam, nskTemp, nskModule, nskType, nskVar, nskLet, nskConst, nskResult, nskProc, nskFunc, nskMethod, nskIterator, nskConverter, nskMacro, nskTemplate, nskField, nskEnumField, nskForVar, nskLabel, nskStub: Source Edit
NimTypeKind = enum ntyNone, ntyBool, ntyChar, ntyEmpty, ntyAlias, ntyNil, ntyExpr, ntyStmt, ntyTypeDesc, ntyGenericInvocation, ntyGenericBody, ntyGenericInst, ntyGenericParam, ntyDistinct, ntyEnum, ntyOrdinal, ntyArray, ntyObject, ntyTuple, ntySet, ntyRange, ntyPtr, ntyRef, ntyVar, ntySequence, ntyProc, ntyPointer, ntyOpenArray, ntyString, ntyCString, ntyForward, ntyInt, ntyInt8, ntyInt16, ntyInt32, ntyInt64, ntyFloat, ntyFloat32, ntyFloat64, ntyFloat128, ntyUInt, ntyUInt8, ntyUInt16, ntyUInt32, ntyUInt64, ntyUnused0, ntyUnused1, ntyUnused2, ntyVarargs, ntyUncheckedArray, ntyError, ntyBuiltinTypeClass, ntyUserTypeClass, ntyUserTypeClassInst, ntyCompositeTypeClass, ntyInferred, ntyAnd, ntyOr, ntyNot, ntyAnything, ntyStatic, ntyFromExpr, ntyOptDeprecated, ntyVoid: Source Edit
TNimSymKinds {....deprecated.} = set[NimSymKind]: Deprecated
Source Edit
TNimTypeKinds {....deprecated.} = set[NimTypeKind]: Deprecated
Source Edit

Consts

AtomicNodes = {nnkNone..nnkNilLit}: Source Edit
CallNodes = {nnkCall, nnkInfix, nnkPrefix, nnkPostfix, nnkCommand, nnkCallStrLit, nnkHiddenCallConv}: Source Edit
nnkCallKinds = {nnkCall, nnkInfix, nnkPrefix, nnkPostfix, nnkCommand, nnkCallStrLit, nnkHiddenCallConv}: Source Edit
nnkLiterals = {nnkCharLit..nnkNilLit}: Source Edit
nnkMutableTy {....deprecated.} = nnkOutTy: Source Edit
nnkSharedTy {....deprecated.} = nnkSinkAsgn: Source Edit
RoutineNodes = {nnkProcDef, nnkFuncDef, nnkMethodDef, nnkDo, nnkLambda, nnkIteratorDef, nnkTemplateDef, nnkConverterDef, nnkMacroDef}: Source Edit

Procs

proc `$`(arg: LineInfo): string {....raises: [], tags: [], forbids: [].}: Return a string representation in the form filepath(line, column). Source Edit
proc `$`(i: NimIdent): string {.magic: "NStrVal", noSideEffect, ...deprecated: "Deprecated since version 0.18.1; Use \'strVal\' instead.", raises: [], tags: [], forbids: [].}: Deprecated: Deprecated since version 0.18.1; Use 'strVal' instead.
Converts a Nim identifier to a string. Source Edit
proc `$`(node: NimNode): string {....raises: [], tags: [], forbids: [].}: Get the string of an identifier node. Source Edit
proc `$`(s: NimSym): string {.magic: "NStrVal", noSideEffect, ...deprecated: "Deprecated since version 0.18.1; Use \'strVal\' instead.", raises: [], tags: [], forbids: [].}: Deprecated: Deprecated since version 0.18.1; Use 'strVal' instead.
Converts a Nim symbol to a string. Source Edit
proc `==`(a, b: NimIdent): bool {.magic: "EqIdent", noSideEffect, ...deprecated: "Deprecated since version 0.18.1; Use \'==\' on \'NimNode\' instead.", raises: [], tags: [], forbids: [].}: Deprecated: Deprecated since version 0.18.1; Use '==' on 'NimNode' instead.
Compares two Nim identifiers. Source Edit
proc `==`(a, b: NimNode): bool {.magic: "EqNimrodNode", noSideEffect, ...raises: [], tags: [], forbids: [].}: Compare two Nim nodes. Return true if nodes are structurally equivalent. This means two independently created nodes can be equal. Source Edit
proc `==`(a, b: NimSym): bool {.magic: "EqNimrodNode", noSideEffect, ...deprecated: "Deprecated since version 0.18.1; Use \'==(NimNode, NimNode)\' instead.", raises: [], tags: [], forbids: [].}: Deprecated: Deprecated since version 0.18.1; Use '==(NimNode, NimNode)' instead.
Compares two Nim symbols. Source Edit
proc `[]`(n: NimNode; i: BackwardsIndex): NimNode {....raises: [], tags: [], forbids: [].}: Get n's i'th child. Source Edit
proc `[]`(n: NimNode; i: int): NimNode {.magic: "NChild", noSideEffect, ...raises: [], tags: [], forbids: [].}: Get n's i'th child. Source Edit
proc `[]`[T, U: Ordinal](n: NimNode; x: HSlice[T, U]): seq[NimNode]: Slice operation for NimNode. Returns a seq of child of n who inclusive range [n[x.a], n[x.b]]. Source Edit
proc `[]=`(n: NimNode; i: BackwardsIndex; child: NimNode) {....raises: [], tags: [], forbids: [].}: Set n's i'th child to child. Source Edit
proc `[]=`(n: NimNode; i: int; child: NimNode) {.magic: "NSetChild", noSideEffect, ...raises: [], tags: [], forbids: [].}: Set n's i'th child to child. Source Edit
proc add(father, child: NimNode): NimNode {.magic: "NAdd", discardable, noSideEffect, ...raises: [], tags: [], forbids: [].}: Adds the child to the father node. Returns the father node so that calls can be nested. Source Edit
proc add(father: NimNode; children: varargs[NimNode]): NimNode {. magic: "NAddMultiple", discardable, noSideEffect, ...raises: [], tags: [], forbids: [].}: Adds each child of children to the father node. Returns the father node so that calls can be nested. Source Edit
proc addIdentIfAbsent(dest: NimNode; ident: string) {....raises: [], tags: [], forbids: [].}: Add ident to dest if it is not present. This is intended for use with pragmas. Source Edit
proc addPragma(someProc, pragma: NimNode) {....raises: [], tags: [], forbids: [].}: Adds pragma to routine definition. Source Edit
proc astGenRepr(n: NimNode): string {....gcsafe, raises: [], tags: [], forbids: [].}: Convert the AST n to the code required to generate that AST.

See also system: repr, treeRepr, and lispRepr.
Source Edit
proc basename(a: NimNode): NimNode {....raises: [], tags: [], forbids: [].}: Pull an identifier from prefix/postfix expressions. Source Edit
proc basename=(a: NimNode; val: string) {....raises: [], tags: [], forbids: [].}: Source Edit
proc bindSym(ident: string | NimNode; rule: BindSymRule = brClosed): NimNode {. magic: "NBindSym", noSideEffect, ...raises: [], tags: [], forbids: [].}: Creates a node that binds ident to a symbol node. The bound symbol may be an overloaded symbol. if ident is a NimNode, it must have nnkIdent kind. If rule == brClosed either an nnkClosedSymChoice tree is returned or nnkSym if the symbol is not ambiguous. If rule == brOpen either an nnkOpenSymChoice tree is returned or nnkSym if the symbol is not ambiguous. If rule == brForceOpen always an nnkOpenSymChoice tree is returned even if the symbol is not ambiguous.

See the manual for more details.
Source Edit
proc body(someProc: NimNode): NimNode {....raises: [], tags: [], forbids: [].}: Source Edit
proc body=(someProc: NimNode; val: NimNode) {....raises: [], tags: [], forbids: [].}: Source Edit
proc boolVal(n: NimNode): bool {.noSideEffect, ...raises: [], tags: [], forbids: [].}: Source Edit
proc callsite(): NimNode {.magic: "NCallSite", ...gcsafe, deprecated: "Deprecated since v0.18.1; use `varargs[untyped]` in the macro prototype instead", raises: [], tags: [], forbids: [].}: Deprecated: Deprecated since v0.18.1; use `varargs[untyped]` in the macro prototype instead
Returns the AST of the invocation expression that invoked this macro. Source Edit
proc copy(node: NimNode): NimNode {....raises: [], tags: [], forbids: [].}: An alias for copyNimTree. Source Edit
proc copyChildrenTo(src, dest: NimNode) {....raises: [], tags: [], forbids: [].}: Copy all children from src to dest. Source Edit
proc copyLineInfo(arg: NimNode; info: NimNode) {.magic: "NLineInfo", noSideEffect, ...raises: [], tags: [], forbids: [].}: Copy lineinfo from info. Source Edit
proc copyNimNode(n: NimNode): NimNode {.magic: "NCopyNimNode", noSideEffect, ...raises: [], tags: [], forbids: [].}: Creates a new AST node by copying the node n. Note that unlike copyNimTree, child nodes of n are not copied.
Example:

macro foo(x: typed) = var s = copyNimNode(x) doAssert s.len == 0 doAssert s.kind == nnkStmtList foo: let x = 12 echo x
Source Edit
proc copyNimTree(n: NimNode): NimNode {.magic: "NCopyNimTree", noSideEffect, ...raises: [], tags: [], forbids: [].}: Creates a new AST node by recursively copying the node n. Note that unlike copyNimNode, this copies n, the children of n, etc.
Example:

macro foo(x: typed) = var s = copyNimTree(x) doAssert s.len == 2 doAssert s.kind == nnkStmtList foo: let x = 12 echo x
Source Edit
proc del(father: NimNode; idx = 0; n = 1) {.magic: "NDel", noSideEffect, ...raises: [], tags: [], forbids: [].}: Deletes n children of father starting at index idx. Source Edit
proc eqIdent(a: NimNode; b: NimNode): bool {.magic: "EqIdent", noSideEffect, ...raises: [], tags: [], forbids: [].}: Style insensitive comparison. a and b can be an identifier or a symbol. Both may be wrapped in an export marker (nnkPostfix) or quoted with backticks (nnkAccQuoted), these nodes will be unwrapped. Source Edit
proc eqIdent(a: NimNode; b: string): bool {.magic: "EqIdent", noSideEffect, ...raises: [], tags: [], forbids: [].}: Style insensitive comparison. a can be an identifier or a symbol. a may be wrapped in an export marker (nnkPostfix) or quoted with backticks (nnkAccQuoted), these nodes will be unwrapped. Source Edit
proc eqIdent(a: string; b: NimNode): bool {.magic: "EqIdent", noSideEffect, ...raises: [], tags: [], forbids: [].}: Style insensitive comparison. b can be an identifier or a symbol. b may be wrapped in an export marker (nnkPostfix) or quoted with backticks (nnkAccQuoted), these nodes will be unwrapped. Source Edit
proc eqIdent(a: string; b: string): bool {.magic: "EqIdent", noSideEffect, ...raises: [], tags: [], forbids: [].}: Style insensitive comparison. Source Edit
proc error(msg: string; n: NimNode = nil) {.magic: "NError", ...gcsafe, noreturn, ...raises: [], tags: [], forbids: [].}: Writes an error message at compile time. The optional n: NimNode parameter is used as the source for file and line number information in the compilation error message. Source Edit
proc expectIdent(n: NimNode; name: string) {....raises: [], tags: [], forbids: [].}: Check that eqIdent(n,name) holds true. If this is not the case, compilation aborts with an error message. This is useful for writing macros that check the AST that is passed to them. Source Edit
proc expectKind(n: NimNode; k: NimNodeKind) {....raises: [], tags: [], forbids: [].}: Checks that n is of kind k. If this is not the case, compilation aborts with an error message. This is useful for writing macros that check the AST that is passed to them. Source Edit
proc expectKind(n: NimNode; k: set[NimNodeKind]) {....raises: [], tags: [], forbids: [].}: Checks that n is of kind k. If this is not the case, compilation aborts with an error message. This is useful for writing macros that check the AST that is passed to them. Source Edit
proc expectLen(n: NimNode; len: int) {....raises: [], tags: [], forbids: [].}: Checks that n has exactly len children. If this is not the case, compilation aborts with an error message. This is useful for writing macros that check its number of arguments. Source Edit
proc expectLen(n: NimNode; min, max: int) {....raises: [], tags: [], forbids: [].}: Checks that n has a number of children in the range min..max. If this is not the case, compilation aborts with an error message. This is useful for writing macros that check its number of arguments. Source Edit
proc expectMinLen(n: NimNode; min: int) {....raises: [], tags: [], forbids: [].}: Checks that n has at least min children. If this is not the case, compilation aborts with an error message. This is useful for writing macros that check its number of arguments. Source Edit
proc extractDocCommentsAndRunnables(n: NimNode): NimNode {....raises: [], tags: [], forbids: [].}: returns a nnkStmtList containing the top-level doc comments and runnableExamples in a, stopping at the first child that is neither. Example:

import std/macros macro transf(a): untyped = result = quote do: proc fun2*() = discard let header = extractDocCommentsAndRunnables(a.body) # correct usage: rest is appended result.body = header result.body.add quote do: discard # just an example # incorrect usage: nesting inside a nnkStmtList: # result.body = quote do: (`header`; discard) proc fun*() {.transf.} = ## first comment runnableExamples: discard runnableExamples: discard ## last comment discard # first statement after doc comments + runnableExamples ## not docgen'd
Source Edit
proc floatVal(n: NimNode): BiggestFloat {.magic: "NFloatVal", noSideEffect, ...raises: [], tags: [], forbids: [].}: Returns a float from any floating point literal. Source Edit
proc floatVal=(n: NimNode; val: BiggestFloat) {.magic: "NSetFloatVal", noSideEffect, ...raises: [], tags: [], forbids: [].}: Source Edit
proc genSym(kind: NimSymKind = nskLet; ident = ""): NimNode {.magic: "NGenSym", noSideEffect, ...raises: [], tags: [], forbids: [].}: Generates a fresh symbol that is guaranteed to be unique. The symbol needs to occur in a declaration context. Source Edit
proc getAlign(arg: NimNode): int {.magic: "NSizeOf", noSideEffect, ...raises: [], tags: [], forbids: [].}: Returns the same result as system.alignof if the alignment is known by the Nim compiler. It works on NimNode for use in macro context. Returns a negative value if the Nim compiler does not know the alignment. Source Edit
proc getAst(macroOrTemplate: untyped): NimNode {.magic: "ExpandToAst", noSideEffect, ...raises: [], tags: [], forbids: [].}: Obtains the AST nodes returned from a macro or template invocation. See also genasts.genAst. Example:

macro FooMacro() = var ast = getAst(BarTemplate())
Source Edit
proc getImpl(s: NimSym): NimNode {.magic: "GetImpl", noSideEffect, ...deprecated: "use `getImpl: NimNode -> NimNode` instead", raises: [], tags: [], forbids: [].}: Deprecated: use `getImpl: NimNode -> NimNode` instead
Source Edit
proc getImpl(symbol: NimNode): NimNode {.magic: "GetImpl", noSideEffect, ...raises: [], tags: [], forbids: [].}: Returns a copy of the declaration of a symbol or nil. Source Edit
proc getImplTransformed(symbol: NimNode): NimNode {.magic: "GetImplTransf", noSideEffect, ...raises: [], tags: [], forbids: [].}: For a typed proc returns the AST after transformation pass; this is useful for debugging how the compiler transforms code (e.g.: defer, for) but note that code transformations are implementation dependent and subject to change. See an example in tests/macros/tmacros_various.nim. Source Edit
proc getOffset(arg: NimNode): int {.magic: "NSizeOf", noSideEffect, ...raises: [], tags: [], forbids: [].}: Returns the same result as system.offsetof if the offset is known by the Nim compiler. It expects a resolved symbol node from a field of a type. Therefore it only requires one argument instead of two. Returns a negative value if the Nim compiler does not know the offset. Source Edit
proc getProjectPath(): string {....raises: [], tags: [], forbids: [].}: Returns the path to the currently compiling project.

This is not to be confused with system.currentSourcePath which returns the path of the source file containing that template call.

For example, assume a dir1/foo.nim that imports a dir2/bar.nim, have the bar.nim print out both getProjectPath and currentSourcePath outputs.

Now when foo.nim is compiled, the getProjectPath from bar.nim will return the dir1/ path, while the currentSourcePath will return the path to the bar.nim source file.

Now when bar.nim is compiled directly, the getProjectPath will now return the dir2/ path, and the currentSourcePath will still return the same path, the path to the bar.nim source file.

The path returned by this proc is set at compile time.

See also:

getCurrentDir proc

Source Edit
proc getSize(arg: NimNode): int {.magic: "NSizeOf", noSideEffect, ...raises: [], tags: [], forbids: [].}: Returns the same result as system.sizeof if the size is known by the Nim compiler. Returns a negative value if the Nim compiler does not know the size. Source Edit
proc getType(n: NimNode): NimNode {.magic: "NGetType", noSideEffect, ...raises: [], tags: [], forbids: [].}: With 'getType' you can access the node's type. A Nim type is mapped to a Nim AST too, so it's slightly confusing but it means the same API can be used to traverse types. Recursive types are flattened for you so there is no danger of infinite recursions during traversal. To resolve recursive types, you have to call 'getType' again. To see what kind of type it is, call typeKind on getType's result. Source Edit
proc getType(n: typedesc): NimNode {.magic: "NGetType", noSideEffect, ...raises: [], tags: [], forbids: [].}: Version of getType which takes a typedesc. Source Edit
proc getTypeImpl(n: NimNode): NimNode {.magic: "NGetType", noSideEffect, ...raises: [], tags: [], forbids: [].}: Returns the type of a node in a form matching the implementation of the type. Any intermediate aliases are expanded to arrive at the final type implementation. You can instead use getImpl on a symbol if you want to find the intermediate aliases.
Example:

type Vec[N: static[int], T] = object arr: array[N, T] Vec4[T] = Vec[4, T] Vec4f = Vec4[float32] var a: Vec4f var b: Vec4[float32] var c: Vec[4, float32] macro dumpTypeImpl(x: typed): untyped = newLit(x.getTypeImpl.repr) let t = """ object arr: array[0 .. 3, float32]""" doAssert(dumpTypeImpl(a) == t) doAssert(dumpTypeImpl(b) == t) doAssert(dumpTypeImpl(c) == t)
Source Edit
proc getTypeImpl(n: typedesc): NimNode {.magic: "NGetType", noSideEffect, ...raises: [], tags: [], forbids: [].}: Version of getTypeImpl which takes a typedesc. Source Edit
proc getTypeInst(n: NimNode): NimNode {.magic: "NGetType", noSideEffect, ...raises: [], tags: [], forbids: [].}: Returns the type of a node in a form matching the way the type instance was declared in the code.
Example:

type Vec[N: static[int], T] = object arr: array[N, T] Vec4[T] = Vec[4, T] Vec4f = Vec4[float32] var a: Vec4f var b: Vec4[float32] var c: Vec[4, float32] macro dumpTypeInst(x: typed): untyped = newLit(x.getTypeInst.repr) doAssert(dumpTypeInst(a) == "Vec4f") doAssert(dumpTypeInst(b) == "Vec4[float32]") doAssert(dumpTypeInst(c) == "Vec[4, float32]")
Source Edit
proc getTypeInst(n: typedesc): NimNode {.magic: "NGetType", noSideEffect, ...raises: [], tags: [], forbids: [].}: Version of getTypeInst which takes a typedesc. Source Edit
proc hasArgOfName(params: NimNode; name: string): bool {....raises: [], tags: [], forbids: [].}: Search nnkFormalParams for an argument. Source Edit
proc hint(msg: string; n: NimNode = nil) {.magic: "NHint", ...gcsafe, raises: [], tags: [], forbids: [].}: Writes a hint message at compile time. Source Edit
proc ident(n: NimNode): NimIdent {.magic: "NIdent", noSideEffect, ...deprecated: "Deprecated since version 0.18.1; All functionality is defined on \'NimNode\'.", raises: [], tags: [], forbids: [].}: Deprecated: Deprecated since version 0.18.1; All functionality is defined on 'NimNode'.
Source Edit
proc ident(name: string): NimNode {.magic: "StrToIdent", noSideEffect, ...raises: [], tags: [], forbids: [].}: Create a new ident node from a string. Source Edit
proc ident=(n: NimNode; val: NimIdent) {.magic: "NSetIdent", noSideEffect, ...deprecated: "Deprecated since version 0.18.1; Generate a new \'NimNode\' with \'ident(string)\' instead.", raises: [], tags: [], forbids: [].}: Deprecated: Deprecated since version 0.18.1; Generate a new 'NimNode' with 'ident(string)' instead.
Source Edit
proc infix(a: NimNode; op: string; b: NimNode): NimNode {....raises: [], tags: [], forbids: [].}: Source Edit
proc insert(a: NimNode; pos: int; b: NimNode) {....raises: [], tags: [], forbids: [].}: Insert node b into node a at pos. Source Edit
proc internalErrorFlag(): string {.magic: "NError", noSideEffect, ...raises: [], tags: [], forbids: [].}: Some builtins set an error flag. This is then turned into a proper exception. Note: Ordinary application code should not call this. Source Edit
proc intVal(n: NimNode): BiggestInt {.magic: "NIntVal", noSideEffect, ...raises: [], tags: [], forbids: [].}: Returns an integer value from any integer literal or enum field symbol. Source Edit
proc intVal=(n: NimNode; val: BiggestInt) {.magic: "NSetIntVal", noSideEffect, ...raises: [], tags: [], forbids: [].}: Source Edit
proc isExported(n: NimNode): bool {.noSideEffect, ...raises: [], tags: [], forbids: [].}: Returns whether the symbol is exported or not. Source Edit
proc isInstantiationOf(instanceProcSym, genProcSym: NimNode): bool {. magic: "SymIsInstantiationOf", noSideEffect, ...raises: [], tags: [], forbids: [].}: Checks if a proc symbol is an instance of the generic proc symbol. Useful to check proc symbols against generic symbols returned by bindSym. Source Edit
proc kind(n: NimNode): NimNodeKind {.magic: "NKind", noSideEffect, ...raises: [], tags: [], forbids: [].}: Returns the kind of the node n. Source Edit
proc last(node: NimNode): NimNode {....raises: [], tags: [], forbids: [].}: Return the last item in nodes children. Same as node[^1]. Source Edit
proc len(n: NimNode): int {.magic: "NLen", noSideEffect, ...raises: [], tags: [], forbids: [].}: Returns the number of children of n. Source Edit
proc lineInfo(arg: NimNode): string {....raises: [], tags: [], forbids: [].}: Return line info in the form filepath(line, column). Source Edit
proc lineInfoObj(n: NimNode): LineInfo {....raises: [], tags: [], forbids: [].}: Returns LineInfo of n, using absolute path for filename. Source Edit
proc lispRepr(n: NimNode; indented = false): string {....gcsafe, raises: [], tags: [], forbids: [].}: Convert the AST n to a human-readable lisp-like string.

See also repr, treeRepr, and astGenRepr.
Source Edit
proc name(someProc: NimNode): NimNode {....raises: [], tags: [], forbids: [].}: Source Edit
proc name=(someProc: NimNode; val: NimNode) {....raises: [], tags: [], forbids: [].}: Source Edit
proc nestList(op: NimNode; pack: NimNode): NimNode {....raises: [], tags: [], forbids: [].}: Nests the list pack into a tree of call expressions: [a, b, c] is transformed into op(a, op(c, d)). This is also known as fold expression. Source Edit
proc nestList(op: NimNode; pack: NimNode; init: NimNode): NimNode {....raises: [], tags: [], forbids: [].}: Nests the list pack into a tree of call expressions: [a, b, c] is transformed into op(a, op(c, d)). This is also known as fold expression. Source Edit
proc newAssignment(lhs, rhs: NimNode): NimNode {....raises: [], tags: [], forbids: [].}: Source Edit
proc newBlockStmt(body: NimNode): NimNode {....raises: [], tags: [], forbids: [].}: Create a new block: stmt. Source Edit
proc newBlockStmt(label, body: NimNode): NimNode {....raises: [], tags: [], forbids: [].}: Create a new block statement with label. Source Edit
proc newCall(theProc: NimIdent; args: varargs[NimNode]): NimNode {....deprecated: "Deprecated since v0.18.1; use \'newCall(string, ...)\' or \'newCall(NimNode, ...)\' instead", raises: [], tags: [], forbids: [].}: Deprecated: Deprecated since v0.18.1; use 'newCall(string, ...)' or 'newCall(NimNode, ...)' instead
Produces a new call node. theProc is the proc that is called with the arguments args[0..]. Source Edit
proc newCall(theProc: NimNode; args: varargs[NimNode]): NimNode {....raises: [], tags: [], forbids: [].}: Produces a new call node. theProc is the proc that is called with the arguments args[0..]. Source Edit
proc newCall(theProc: string; args: varargs[NimNode]): NimNode {....raises: [], tags: [], forbids: [].}: Produces a new call node. theProc is the proc that is called with the arguments args[0..]. Source Edit
proc newColonExpr(a, b: NimNode): NimNode {....raises: [], tags: [], forbids: [].}: Create new colon expression. newColonExpr(a, b) -> a: b Source Edit
proc newCommentStmtNode(s: string): NimNode {.noSideEffect, ...raises: [], tags: [], forbids: [].}: Creates a comment statement node. Source Edit
proc newConstStmt(name, value: NimNode): NimNode {....raises: [], tags: [], forbids: [].}: Create a new const stmt. Source Edit
proc newDotExpr(a, b: NimNode): NimNode {....raises: [], tags: [], forbids: [].}: Create new dot expression. a.dot(b) -> a.b Source Edit
proc newEmptyNode(): NimNode {.noSideEffect, ...raises: [], tags: [], forbids: [].}: Create a new empty node. Source Edit
proc newEnum(name: NimNode; fields: openArray[NimNode]; public, pure: bool): NimNode {. ...raises: [], tags: [], forbids: [].}: Creates a new enum. name must be an ident. Fields are allowed to be either idents or EnumFieldDef:

newEnum( name = ident("Colors"), fields = [ident("Blue"), ident("Red")], public = true, pure = false) # type Colors* = Blue Red
Source Edit
proc newFloatLitNode(f: BiggestFloat): NimNode {....raises: [], tags: [], forbids: [].}: Creates a float literal node from f. Source Edit
proc newIdentDefs(name, kind: NimNode; default = newEmptyNode()): NimNode {. ...raises: [], tags: [], forbids: [].}: Creates a new nnkIdentDefs node of a specific kind and value.

nnkIdentDefs need to have at least three children, but they can have more: first comes a list of identifiers followed by a type and value nodes. This helper proc creates a three node subtree, the first subnode being a single identifier name. Both the kind node and default (value) nodes may be empty depending on where the nnkIdentDefs appears: tuple or object definitions will have an empty default node, let or var blocks may have an empty kind node if the identifier is being assigned a value. Example:

var varSection = newNimNode(nnkVarSection).add( newIdentDefs(ident("a"), ident("string")), newIdentDefs(ident("b"), newEmptyNode(), newLit(3))) # --> var # a: string # b = 3

If you need to create multiple identifiers you need to use the lower level newNimNode:

result = newNimNode(nnkIdentDefs).add( ident("a"), ident("b"), ident("c"), ident("string"), newStrLitNode("Hello"))
Source Edit
proc newIdentNode(i: NimIdent): NimNode {....deprecated: "use ident(string)", raises: [], tags: [], forbids: [].}: Deprecated: use ident(string)
Creates an identifier node from i. Source Edit
proc newIdentNode(i: string): NimNode {.magic: "StrToIdent", noSideEffect, ...raises: [], tags: [], forbids: [].}: Creates an identifier node from i. It is simply an alias for ident(string). Use that, it's shorter. Source Edit
proc newIfStmt(branches: varargs[tuple[cond, body: NimNode]]): NimNode {. ...raises: [], tags: [], forbids: [].}: Constructor for if statements.

newIfStmt( (Ident, StmtList), ... )
Source Edit
proc newIntLitNode(i: BiggestInt): NimNode {....raises: [], tags: [], forbids: [].}: Creates an int literal node from i. Source Edit
proc newLetStmt(name, value: NimNode): NimNode {....raises: [], tags: [], forbids: [].}: Create a new let stmt. Source Edit
proc newLit(arg: enum): NimNode: Source Edit
proc newLit(arg: object): NimNode: Source Edit
proc newLit(arg: ref object): NimNode: produces a new ref type literal node. Source Edit
proc newLit(b: bool): NimNode {....raises: [], tags: [], forbids: [].}: Produces a new boolean literal node. Source Edit
proc newLit(c: char): NimNode {....raises: [], tags: [], forbids: [].}: Produces a new character literal node. Source Edit
proc newLit(f: float32): NimNode {....raises: [], tags: [], forbids: [].}: Produces a new float literal node. Source Edit
proc newLit(f: float64): NimNode {....raises: [], tags: [], forbids: [].}: Produces a new float literal node. Source Edit
proc newLit(i: int): NimNode {....raises: [], tags: [], forbids: [].}: Produces a new integer literal node. Source Edit
proc newLit(i: int8): NimNode {....raises: [], tags: [], forbids: [].}: Produces a new integer literal node. Source Edit
proc newLit(i: int16): NimNode {....raises: [], tags: [], forbids: [].}: Produces a new integer literal node. Source Edit
proc newLit(i: int32): NimNode {....raises: [], tags: [], forbids: [].}: Produces a new integer literal node. Source Edit
proc newLit(i: int64): NimNode {....raises: [], tags: [], forbids: [].}: Produces a new integer literal node. Source Edit
proc newLit(i: uint): NimNode {....raises: [], tags: [], forbids: [].}: Produces a new unsigned integer literal node. Source Edit
proc newLit(i: uint8): NimNode {....raises: [], tags: [], forbids: [].}: Produces a new unsigned integer literal node. Source Edit
proc newLit(i: uint16): NimNode {....raises: [], tags: [], forbids: [].}: Produces a new unsigned integer literal node. Source Edit
proc newLit(i: uint32): NimNode {....raises: [], tags: [], forbids: [].}: Produces a new unsigned integer literal node. Source Edit
proc newLit(i: uint64): NimNode {....raises: [], tags: [], forbids: [].}: Produces a new unsigned integer literal node. Source Edit
proc newLit(s: string): NimNode {....raises: [], tags: [], forbids: [].}: Produces a new string literal node. Source Edit
proc newLit[N, T](arg: array[N, T]): NimNode: Source Edit
proc newLit[T: tuple](arg: T): NimNode: Source Edit
proc newLit[T](arg: seq[T]): NimNode: Source Edit
proc newLit[T](s: set[T]): NimNode: Source Edit
proc newNilLit(): NimNode {....raises: [], tags: [], forbids: [].}: New nil literal shortcut. Source Edit
proc newNimNode(kind: NimNodeKind; lineInfoFrom: NimNode = nil): NimNode {. magic: "NNewNimNode", noSideEffect, ...raises: [], tags: [], forbids: [].}: Creates a new AST node of the specified kind.

The lineInfoFrom parameter is used for line information when the produced code crashes. You should ensure that it is set to a node that you are transforming.
Source Edit
proc newPar(exprs: NimNode): NimNode {....raises: [], tags: [], forbids: [].}: Create a new parentheses-enclosed expression. Source Edit
proc newPar(exprs: varargs[NimNode]): NimNode {....deprecated: "don\'t use newPar/nnkPar to construct tuple expressions; use nnkTupleConstr instead", raises: [], tags: [], forbids: [].}: Deprecated: don't use newPar/nnkPar to construct tuple expressions; use nnkTupleConstr instead
Create a new parentheses-enclosed expression. Source Edit
proc newProc(name = newEmptyNode(); params: openArray[NimNode] = [newEmptyNode()]; body: NimNode = newStmtList(); procType = nnkProcDef; pragmas: NimNode = newEmptyNode()): NimNode {....raises: [], tags: [], forbids: [].}: Shortcut for creating a new proc.

The params array must start with the return type of the proc, followed by a list of IdentDefs which specify the params.
Source Edit
proc newStmtList(stmts: varargs[NimNode]): NimNode {....raises: [], tags: [], forbids: [].}: Create a new statement list. Source Edit
proc newStrLitNode(s: string): NimNode {.noSideEffect, ...raises: [], tags: [], forbids: [].}: Creates a string literal node from s. Source Edit
proc newTree(kind: NimNodeKind; children: varargs[NimNode]): NimNode {. ...raises: [], tags: [], forbids: [].}: Produces a new node with children. Source Edit
proc newVarStmt(name, value: NimNode): NimNode {....raises: [], tags: [], forbids: [].}: Create a new var stmt. Source Edit
proc nodeID(n: NimNode): int {.magic: "NodeId", ...raises: [], tags: [], forbids: [].}: Returns the id of n, when the compiler has been compiled with the flag -d:useNodeids, otherwise returns -1. This proc is for the purpose to debug the compiler only. Source Edit
proc owner(sym: NimNode): NimNode {.magic: "SymOwner", noSideEffect, ...deprecated, raises: [], tags: [], forbids: [].}: Deprecated

Accepts a node of kind nnkSym and returns its owner's symbol. The meaning of 'owner' depends on sym's NimSymKind and declaration context. For top level declarations this is an nskModule symbol, for proc local variables an nskProc symbol, for enum/object fields an nskType symbol, etc. For symbols without an owner, nil is returned.

See also:

symKind proc to get the kind of a symbol

getImpl proc to get the declaration of a symbol

Source Edit
proc params(someProc: NimNode): NimNode {....raises: [], tags: [], forbids: [].}: Source Edit
proc params=(someProc: NimNode; params: NimNode) {....raises: [], tags: [], forbids: [].}: Source Edit
proc parseExpr(s: string; filename: string = ""): NimNode {.noSideEffect, ...raises: [ValueError], tags: [], forbids: [].}: Compiles the passed string to its AST representation. Expects a single expression. Raises ValueError for parsing errors. A filename can be given for more informative errors. Source Edit
proc parseStmt(s: string; filename: string = ""): NimNode {.noSideEffect, ...raises: [ValueError], tags: [], forbids: [].}: Compiles the passed string to its AST representation. Expects one or more statements. Raises ValueError for parsing errors. A filename can be given for more informative errors. Source Edit
proc postfix(node: NimNode; op: string): NimNode {....raises: [], tags: [], forbids: [].}: Source Edit
proc pragma(someProc: NimNode): NimNode {....raises: [], tags: [], forbids: [].}: Get the pragma of a proc type. These will be expanded. Source Edit
proc pragma=(someProc: NimNode; val: NimNode) {....raises: [], tags: [], forbids: [].}: Set the pragma of a proc type. Source Edit
proc prefix(node: NimNode; op: string): NimNode {....raises: [], tags: [], forbids: [].}: Source Edit
proc quote(bl: typed; op = "``"): NimNode {.magic: "QuoteAst", noSideEffect, ...raises: [], tags: [], forbids: [].}: Quasi-quoting operator. Accepts an expression or a block and returns the AST that represents it. Within the quoted AST, you are able to interpolate NimNode expressions from the surrounding scope. If no operator is given, quoting is done using backticks. Otherwise, the given operator must be used as a prefix operator for any interpolated expression. The original meaning of the interpolation operator may be obtained by escaping it (by prefixing it with itself) when used as a unary operator: e.g. @ is escaped as @@, &% is escaped as &%&% and so on; see examples.

A custom operator interpolation needs accent quoted (``) whenever it resolves to a symbol.

See also genasts which avoids some issues with quote.

Example:

macro check(ex: untyped) = # this is a simplified version of the check macro from the # unittest module. # If there is a failed check, we want to make it easy for # the user to jump to the faulty line in the code, so we # get the line info here: var info = ex.lineinfo # We will also display the code string of the failed check: var expString = ex.toStrLit # Finally we compose the code to implement the check: result = quote do: if not `ex`: echo `info` & ": Check failed: " & `expString` check 1 + 1 == 2

Example:

# example showing how to define a symbol that requires backtick without # quoting it. var destroyCalled = false macro bar() = let s = newTree(nnkAccQuoted, ident"=destroy") # let s = ident"`=destroy`" # this would not work result = quote do: type Foo = object # proc `=destroy`(a: var Foo) = destroyCalled = true # this would not work proc `s`(a: var Foo) = destroyCalled = true block: let a = Foo() bar() doAssert destroyCalled

Example:

# custom `op` var destroyCalled = false macro bar(ident) = var x = 1.5 result = quote("@") do: type Foo = object let `@ident` = 0 # custom op interpolated symbols need quoted (``) proc `=destroy`(a: var Foo) = doAssert @x == 1.5 doAssert compiles(@x == 1.5) let b1 = @[1,2] let b2 = @@[1,2] doAssert $b1 == "[1, 2]" doAssert $b2 == "@[1, 2]" destroyCalled = true block: let a = Foo() bar(someident) doAssert destroyCalled proc `&%`(x: int): int = 1 proc `&%`(x, y: int): int = 2 macro bar2() = var x = 3 result = quote("&%") do: var y = &%x # quoting operator doAssert &%&%y == 1 # unary operator => need to escape doAssert y &% y == 2 # binary operator => no need to escape doAssert y == 3 bar2()
Source Edit
proc sameType(a, b: NimNode): bool {.magic: "SameNodeType", noSideEffect, ...raises: [], tags: [], forbids: [].}: Compares two Nim nodes' types. Return true if the types are the same, e.g. true when comparing alias with original type. Source Edit
proc setLineInfo(arg: NimNode; file: string; line: int; column: int) {. ...raises: [], tags: [], forbids: [].}: Sets the line info on the NimNode. The file needs to exists, but can be a relative path. If you want to attach line info to a block using quote you'll need to add the line information after the quote block. Source Edit
proc setLineInfo(arg: NimNode; lineInfo: LineInfo) {....raises: [], tags: [], forbids: [].}: See setLineInfo proc Source Edit
proc signatureHash(n: NimNode): string {.magic: "NSigHash", noSideEffect, ...raises: [], tags: [], forbids: [].}: Returns a stable identifier derived from the signature of a symbol. The signature combines many factors such as the type of the symbol, the owning module of the symbol and others. The same identifier is used in the back-end to produce the mangled symbol name. Source Edit
proc strVal(n: NimNode): string {.magic: "NStrVal", noSideEffect, ...raises: [], tags: [], forbids: [].}: Returns the string value of an identifier, symbol, comment, or string literal.

See also:

strVal= proc for setting the string value.

Source Edit
proc strVal=(n: NimNode; val: string) {.magic: "NSetStrVal", noSideEffect, ...raises: [], tags: [], forbids: [].}: Sets the string value of a string literal or comment. Setting strVal is disallowed for nnkIdent and nnkSym nodes; a new node must be created using ident or bindSym instead.

See also:

strVal proc for getting the string value.

ident proc for creating an identifier.

bindSym proc for binding a symbol.

Source Edit
proc symBodyHash(s: NimNode): string {.noSideEffect, ...raises: [], tags: [], forbids: [].}: Returns a stable digest for symbols derived not only from type signature and owning module, but also implementation body. All procs/variables used in the implementation of this symbol are hashed recursively as well, including magics from system module. Source Edit
proc symbol(n: NimNode): NimSym {.magic: "NSymbol", noSideEffect, ...deprecated: "Deprecated since version 0.18.1; All functionality is defined on \'NimNode\'.", raises: [], tags: [], forbids: [].}: Deprecated: Deprecated since version 0.18.1; All functionality is defined on 'NimNode'.
Source Edit
proc symbol=(n: NimNode; val: NimSym) {.magic: "NSetSymbol", noSideEffect, ...deprecated: "Deprecated since version 0.18.1; Generate a new \'NimNode\' with \'genSym\' instead.", raises: [], tags: [], forbids: [].}: Deprecated: Deprecated since version 0.18.1; Generate a new 'NimNode' with 'genSym' instead.
Source Edit
proc symKind(symbol: NimNode): NimSymKind {.magic: "NSymKind", noSideEffect, ...raises: [], tags: [], forbids: [].}: Source Edit
proc toNimIdent(s: string): NimIdent {.magic: "StrToIdent", noSideEffect, ...deprecated: "Deprecated since version 0.18.0: Use \'ident\' or \'newIdentNode\' instead.", raises: [], tags: [], forbids: [].}: Deprecated: Deprecated since version 0.18.0: Use 'ident' or 'newIdentNode' instead.
Constructs an identifier from the string s. Source Edit
proc toStrLit(n: NimNode): NimNode {....raises: [], tags: [], forbids: [].}: Converts the AST n to the concrete Nim code and wraps that in a string literal node. Source Edit
proc treeRepr(n: NimNode): string {....gcsafe, raises: [], tags: [], forbids: [].}: Convert the AST n to a human-readable tree-like string.

See also repr, lispRepr, and astGenRepr.
Source Edit
proc typeKind(n: NimNode): NimTypeKind {.magic: "NGetType", noSideEffect, ...raises: [], tags: [], forbids: [].}: Returns the type kind of the node 'n' that should represent a type, that means the node should have been obtained via getType. Source Edit
proc unpackInfix(node: NimNode): tuple[left: NimNode, op: string, right: NimNode] {. ...raises: [], tags: [], forbids: [].}: Source Edit
proc unpackPostfix(node: NimNode): tuple[node: NimNode, op: string] {. ...raises: [], tags: [], forbids: [].}: Source Edit
proc unpackPrefix(node: NimNode): tuple[node: NimNode, op: string] {....raises: [], tags: [], forbids: [].}: Source Edit
proc warning(msg: string; n: NimNode = nil) {.magic: "NWarning", ...gcsafe, raises: [], tags: [], forbids: [].}: Writes a warning message at compile time. Source Edit

Iterators

iterator children(n: NimNode): NimNode {.inline, ...raises: [], tags: [], forbids: [].}: Iterates over the children of the NimNode n. Source Edit
iterator items(n: NimNode): NimNode {.inline, ...raises: [], tags: [], forbids: [].}: Iterates over the children of the NimNode n. Source Edit
iterator pairs(n: NimNode): (int, NimNode) {.inline, ...raises: [], tags: [], forbids: [].}: Iterates over the children of the NimNode n and its indices. Source Edit

Macros

macro dumpAstGen(s: untyped): untyped: Accepts a block of nim code and prints the parsed abstract syntax tree using the astGenRepr proc. Printing is done at compile time.

You can use this as a tool to write macros quicker by writing example outputs and then copying the snippets into the macro for modification.

For example:

dumpAstGen: echo "Hello, World!"

Outputs:

nnkStmtList.newTree( nnkCommand.newTree( newIdentNode("echo"), newLit("Hello, World!") ) )

Also see dumpTree and dumpLisp.
Source Edit
macro dumpLisp(s: untyped): untyped: Accepts a block of nim code and prints the parsed abstract syntax tree using the lispRepr proc. Printing is done at compile time.

You can use this as a tool to explore the Nim's abstract syntax tree and to discover what kind of nodes must be created to represent a certain expression/statement.

For example:

dumpLisp: echo "Hello, World!"

Outputs:

(StmtList (Command (Ident "echo") (StrLit "Hello, World!")))

Also see dumpAstGen and dumpTree.
Source Edit
macro dumpTree(s: untyped): untyped: Accepts a block of nim code and prints the parsed abstract syntax tree using the treeRepr proc. Printing is done at compile time.

You can use this as a tool to explore the Nim's abstract syntax tree and to discover what kind of nodes must be created to represent a certain expression/statement.

For example:

dumpTree: echo "Hello, World!"

Outputs:

StmtList Command Ident "echo" StrLit "Hello, World!"

Also see dumpAstGen and dumpLisp.
Source Edit
macro expandMacros(body: typed): untyped: Expands one level of macro - useful for debugging. Can be used to inspect what happens when a macro call is expanded, without altering its result.

For instance,

import std/[sugar, macros] let x = 10 y = 20 expandMacros: dump(x + y)

will actually dump x + y, but at the same time will print at compile time the expansion of the dump macro, which in this case is debugEcho ["x + y", " = ", x + y].
Source Edit
macro getCustomPragmaVal(n: typed; cp: typed{nkSym}): untyped: Expands to value of custom pragma cp of expression n which is expected to be nnkDotExpr, a proc or a type.

See also hasCustomPragma.

template serializationKey(key: string) {.pragma.} type MyObj {.serializationKey: "mo".} = object myField {.serializationKey: "mf".}: int var o: MyObj assert(o.myField.getCustomPragmaVal(serializationKey) == "mf") assert(o.getCustomPragmaVal(serializationKey) == "mo") assert(MyObj.getCustomPragmaVal(serializationKey) == "mo")
Source Edit
macro hasCustomPragma(n: typed; cp: typed{nkSym}): untyped: Expands to true if expression n which is expected to be nnkDotExpr (if checking a field), a proc or a type has custom pragma cp.

See also getCustomPragmaVal.

template myAttr() {.pragma.} type MyObj = object myField {.myAttr.}: int proc myProc() {.myAttr.} = discard var o: MyObj assert(o.myField.hasCustomPragma(myAttr)) assert(myProc.hasCustomPragma(myAttr))
Source Edit
macro unpackVarargs(callee: untyped; args: varargs[untyped]): untyped: Calls callee with args unpacked as individual arguments. This is useful in 2 cases:

when forwarding varargs[T] for some typed T

when forwarding varargs[untyped] when args can potentially be empty, due to a compiler limitation

Example:

template call1(fun: typed; args: varargs[untyped]): untyped = unpackVarargs(fun, args) # when varargsLen(args) > 0: fun(args) else: fun() # this would also work template call2(fun: typed; args: varargs[typed]): untyped = unpackVarargs(fun, args) proc fn1(a = 0, b = 1) = discard (a, b) call1(fn1, 10, 11) call1(fn1) # `args` is empty in this case if false: call2(echo, 10, 11) # would print 1011
Source Edit

Templates

template findChild(n: NimNode; cond: untyped): NimNode {.dirty.}: Find the first child node matching condition (or nil).

var res = findChild(n, it.kind == nnkPostfix and it.basename.ident == ident"foo")
Source Edit
template `or`(x, y: NimNode): NimNode: Evaluate x and when it is not an empty node, return it. Otherwise evaluate to y. Can be used to chain several expressions to get the first expression that is not empty.

let node = mightBeEmpty() or mightAlsoBeEmpty() or fallbackNode
Source Edit

std/macros

The AST in Nim

Leaf nodes/Atoms

Calls/expressions

Command call

Call with ()

Infix operator call

Prefix operator call

Postfix operator call

Call with named arguments

Call with raw string literal

Dereference operator []

Addr operator

Cast operator

Object access operator .

Array access operator []

Parentheses

Tuple Constructors

Curly braces

Brackets

Ranges

If expression

Documentation Comments

Pragmas

Statements

If statement

When statement

Assignment

Statement list

Case statement

While statement

For statement

Try statement

Return statement

Yield statement

Discard statement

Continue statement

Break statement

Block statement

Asm statement

Import section

From statement

Export statement

Include statement

Var section

Let section

Const section

Type section

Mixin statement

Bind statement

Procedure declaration

Iterator declaration

Converter declaration

Template declaration

Macro declaration

Hidden Standard Conversion

Special node kinds

Imports

Types

Consts

Procs

Iterators

Macros

Templates

Call with `()`

Dereference operator `[]`

Object access operator `.`

Array access operator `[]`