/Haskell 7


Maintainer [email protected]
Stability experimental
Portability portable (FFI)
Safe Haskell Trustworthy
Language Haskell2010


This module provides a low-level interface to the C functions of the terminfo library.

NOTE: Since this library is built on top of the curses interface, it is not thread-safe.


data Terminal Source

setupTerm :: String -> IO Terminal Source

Initialize the terminfo library to the given terminal entry.

Throws a SetupTermError if the terminfo database could not be read.

setupTermFromEnv :: IO Terminal Source

Initialize the terminfo library, using the TERM environmental variable. If TERM is not set, we use the generic, minimal entry dumb.

Throws a SetupTermError if the terminfo database could not be read.

data SetupTermError Source


data Capability a Source

A feature or operation which a Terminal may define.

getCapability :: Terminal -> Capability a -> Maybe a Source

tiGetFlag :: String -> Capability Bool Source

Look up a boolean capability in the terminfo database.

Unlike tiGuardFlag, this capability never fails; it returns False if the capability is absent or set to false, and returns True otherwise.

tiGuardFlag :: String -> Capability () Source

Look up a boolean capability in the terminfo database, and fail if it's not defined.

tiGetNum :: String -> Capability Int Source

Look up a numeric capability in the terminfo database.

tiGetStr :: String -> Capability String Source

Deprecated: use tiGetOutput instead.

Look up a string capability in the terminfo database. NOTE: This function is deprecated; use tiGetOutput1 instead.


Terminfo contains many string capabilities for special effects. For example, the cuu1 capability moves the cursor up one line; on ANSI terminals this is accomplished by printing the control sequence "\ESC[A". However, some older terminals also require "padding", or short pauses, after certain commands. For example, when TERM=vt100 the cuu1 capability is "\ESC[A$<2>", which instructs terminfo to pause for two milliseconds after outputting the control sequence.

The TermOutput monoid abstracts away all padding and control sequence output. Unfortunately, that datatype is difficult to integrate into existing String-based APIs such as pretty-printers. Thus, as a workaround, tiGetOutput1 also lets us access the control sequences as Strings. The one caveat is that it will not allow you to access padded control sequences as Strings. For example:

> t <- setupTerm "vt100"
> isJust (getCapability t (tiGetOutput1 "cuu1") :: Maybe String)
> isJust (getCapability t (tiGetOutput1 "cuu1") :: Maybe TermOutput)

String capabilities will work with software-based terminal types such as xterm and linux. However, you should use TermOutput if compatibility with older terminals is important. Additionally, the visualBell capability which flashes the screen usually produces its effect with a padding directive, so it will only work with TermOutput.

tiGetOutput1 :: forall f. OutputCap f => String -> Capability f Source

Look up an output capability which takes a fixed number of parameters (for example, Int -> Int -> TermOutput).

For capabilities which may contain variable-length padding, use tiGetOutput instead.

class OutputCap f Source

Minimal complete definition

hasOkPadding, outputCap


class (Monoid s, OutputCap s) => TermStr s Source


data TermOutput Source

An action which sends output to the terminal. That output may mix plain text with control characters and escape sequences, along with delays (called "padding") required by some older terminals.

runTermOutput :: Terminal -> TermOutput -> IO () Source

Write the terminal output to the standard output device.

hRunTermOutput :: Handle -> Terminal -> TermOutput -> IO () Source

Write the terminal output to the terminal or file managed by the given Handle.

termText :: String -> TermOutput Source

tiGetOutput :: String -> Capability ([Int] -> LinesAffected -> TermOutput) Source

Look up an output capability in the terminfo database.

type LinesAffected = Int Source

A parameter to specify the number of lines affected. Some capabilities (e.g., clear and dch1) use this parameter on some terminals to compute variable-length padding.

Monoid functions

class Monoid a where Source

The class of monoids (types with an associative binary operation that has an identity). Instances should satisfy the following laws:

  • mappend mempty x = x
  • mappend x mempty = x
  • mappend x (mappend y z) = mappend (mappend x y) z
  • mconcat = foldr mappend mempty

The method names refer to the monoid of lists under concatenation, but there are many other instances.

Some types can be viewed as a monoid in more than one way, e.g. both addition and multiplication on numbers. In such cases we often define newtypes and make those instances of Monoid, e.g. Sum and Product.

Minimal complete definition

mempty, mappend


mempty :: a Source

Identity of mappend

mappend :: a -> a -> a Source

An associative operation

mconcat :: [a] -> a Source

Fold a list using the monoid. For most types, the default definition for mconcat will be used, but the function is included in the class definition so that an optimized version can be provided for specific types.


Monoid Ordering
Monoid ()
Monoid TermOutput
Monoid [a]
Ord a => Monoid (Max a)
Ord a => Monoid (Min a)
Monoid a => Monoid (Maybe a)

Lift a semigroup into Maybe forming a Monoid according to http://en.wikipedia.org/wiki/Monoid: "Any semigroup S may be turned into a monoid simply by adjoining an element e not in S and defining e*e = e and e*s = s = s*e for all s ∈ S." Since there is no "Semigroup" typeclass providing just mappend, we use Monoid instead.

Monoid b => Monoid (a -> b)
(Monoid a, Monoid b) => Monoid (a, b)
Monoid a => Monoid (Const a b)
Monoid (Proxy k s)
(Monoid a, Monoid b, Monoid c) => Monoid (a, b, c)
(Monoid a, Monoid b, Monoid c, Monoid d) => Monoid (a, b, c, d)
(Monoid a, Monoid b, Monoid c, Monoid d, Monoid e) => Monoid (a, b, c, d, e)

(<#>) :: Monoid m => m -> m -> m infixl 2 Source

An operator version of mappend.

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Licensed under a BSD-style license (see top of the page).