| Copyright | Nils Anders Danielsson 2006 Alexander Berntsen 2014 | 
|---|---|
| License | BSD-style (see the LICENSE file in the distribution) | 
| Maintainer | libraries@haskell.org | 
| Stability | experimental | 
| Portability | portable | 
| Safe Haskell | Trustworthy | 
| Language | Haskell2010 | 
Data.Function
Contents
- Prelude re-exports
- Other combinators
Description
Simple combinators working solely on and with functions.
Prelude re-exports
const x is a unary function which evaluates to x for all inputs.
>>>const 42 "hello"42
>>>map (const 42) [0..3][42,42,42,42]
flip :: (a -> b -> c) -> b -> a -> c #
flip ff.
>>>flip (++) "hello" "world""worldhello"
($) :: forall r a (b :: TYPE r). (a -> b) -> a -> b infixr 0 #
Application operator.  This operator is redundant, since ordinary
 application (f x) means the same as (f . However, $ x)$ has
 low, right-associative binding precedence, so it sometimes allows
 parentheses to be omitted; for example:
f $ g $ h x = f (g (h x))
It is also useful in higher-order situations, such as map ($ 0) xszipWith ($) fs xs
Note that ( is levity-polymorphic in its result type, so that
 $)foo  where $ Truefoo :: Bool -> Int# is well-typed.
Other combinators
fix ff,
 i.e. the least defined x such that f x = x.
For example, we can write the factorial function using direct recursion as
>>>let fac n = if n <= 1 then 1 else n * fac (n-1) in fac 5120
This uses the fact that Haskell’s let introduces recursive bindings. We can
 rewrite this definition using fix,
>>>fix (\rec n -> if n <= 1 then 1 else n * rec (n-1)) 5120
Instead of making a recursive call, we introduce a dummy parameter rec;
 when used within fix, this parameter then refers to fix’s argument, hence
 the recursion is reintroduced.