Template Haskell supports quasiquoting, which permits users to construct program fragments by directly writing concrete syntax. A quasiquoter is essentially a function with takes a string to a Template Haskell AST. This module defines the
QuasiQuoter datatype, which specifies a quasiquoter
q which can be invoked using the syntax
[q| ... string to parse ... |] when the
QuasiQuotes language extension is enabled, and some utility functions for manipulating quasiquoters. Nota bene: this package does not define any parsers, that is up to you.
data QuasiQuoter Source
QuasiQuoter type, a value
q of this type can be used in the syntax
[q| ... string to parse ...|]. In fact, for convenience, a
QuasiQuoter actually defines multiple quasiquoters to be used in different splice contexts; if you are only interested in defining a quasiquoter to be used for expressions, you would define a
QuasiQuoter with only
quoteExp, and leave the other fields stubbed out with errors.
quoteFile :: QuasiQuoter -> QuasiQuoter Source
quoteFile takes a
QuasiQuoter and lifts it into one that read the data out of a file. For example, suppose
asmq is an assembly-language quoter, so that you can write [asmq| ld r1, r2 |] as an expression. Then if you define
asmq_f = quoteFile asmq, then the quote [asmq_f|foo.s|] will take input from file
"foo.s" instead of the inline text
dataToQa :: forall a k q. Data a => (Name -> k) -> (Lit -> Q q) -> (k -> [Q q] -> Q q) -> (forall b. Data b => b -> Maybe (Q q)) -> a -> Q q Source
dataToQa is an internal utility function for constructing generic conversion functions from types with
Data instances to various quasi-quoting representations. See the source of
dataToPatQ for two example usages:
appQ are overloadable to account for different syntax for expressions and patterns;
antiQ allows you to override type-specific cases, a common usage is just
const Nothing, which results in no overloading.
dataToExpQ :: Data a => (forall b. Data b => b -> Maybe (Q Exp)) -> a -> Q Exp Source
dataToExpQ converts a value to a 'Q Exp' representation of the same value, in the SYB style. It is generalized to take a function override type-specific cases; see
liftData for a more commonly used variant.
dataToPatQ :: Data a => (forall b. Data b => b -> Maybe (Q Pat)) -> a -> Q Pat Source
dataToPatQ converts a value to a 'Q Pat' representation of the same value, in the SYB style. It takes a function to handle type-specific cases, alternatively, pass
const Nothing to get default behavior.
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