When should I use $ (and can it always be replaced with parentheses)?

Question

From what I\'m reading, $ is described as \"applies a function to its arguments.\" However, it doesn\'t seem to work quite like (apply ...) in Lisp

Answer 1

The documentation of ($) answers your question. Unfortunately it isn't listed in the automatically generated documentation of the Prelude.

However it is listed in the sourcecode which you can find here:

http://darcs.haskell.org/packages/base/Prelude.hs

However this module doesn't define ($) directly. The following, which is imported by the former, does:

http://darcs.haskell.org/packages/base/GHC/Base.lhs

I included the relevant code below:

infixr 0  $

...

-- | Application operator.  This operator is redundant, since ordinary
-- application @(f x)@ means the same as @(f '$' x)@. However, '$' 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' ('$' 0) xs@,
-- or @'Data.List.zipWith' ('$') fs xs@.
{-# INLINE ($) #-}
($)                     :: (a -> b) -> a -> b
f $ x                   =  f x