Miscellany.hs

-----------------------------------------------------------------------------------------
-- |
-- Module      :  FRP.Yampa.Miscellany
-- Copyright   :  (c) Antony Courtney and Henrik Nilsson, Yale University, 2003
-- License     :  BSD-style (see the LICENSE file in the distribution)
--
-- Maintainer  :  nilsson@cs.yale.edu
-- Stability   :  provisional
-- Portability :  portable
--
-- Collection of entities that really should be part
-- of the Haskell 98 prelude or simply have no better
-- home.
--
-- !!! Reverse function composition should go.
-- !!! Better to use '<<<' and '>>>' for, respectively,
-- !!! function composition and reverse function composition.
--
-----------------------------------------------------------------------------------------

module FRP.Yampa.Miscellany (
-- Reverse function composition
    ( # ),	-- :: (a -> b) -> (b -> c) -> (a -> c),	infixl 9

-- Arrow plumbing aids
    dup,	-- :: a -> (a,a)
    swap,	-- :: (a,b) -> (b,a)

-- Maps over lists of pairs
    mapFst,	-- :: (a -> b) -> [(a,c)] -> [(b,c)]
    mapSnd,	-- :: (a -> b) -> [(c,a)] -> [(c,b)]

-- Generalized tuple selectors
    sel3_1, sel3_2, sel3_3,
    sel4_1, sel4_2, sel4_3, sel4_4,
    sel5_1, sel5_2, sel5_3, sel5_4, sel5_5,

-- Floating point utilities
    fDiv,	-- :: (RealFrac a, Integral b) => a -> a -> b
    fMod,	-- :: RealFrac a => a -> a -> a
    fDivMod	-- :: (RealFrac a, Integral b) => a -> a -> (b, a)
) where

infixl 9 #
infixl 7 `fDiv`, `fMod`


------------------------------------------------------------------------------
-- Reverse function composition
------------------------------------------------------------------------------

-- !!! Reverse function composition should go.
-- !!! Better to use <<< and >>> for, respectively,
-- !!! function composition and reverse function composition.

( # ) :: (a -> b) -> (b -> c) -> (a -> c)
f # g = g . f


------------------------------------------------------------------------------
-- Arrow plumbing aids
------------------------------------------------------------------------------

dup :: a -> (a,a)
dup x = (x,x)

swap :: (a,b) -> (b,a)
swap ~(x,y) = (y,x)


------------------------------------------------------------------------------
-- Maps over lists of pairs
------------------------------------------------------------------------------

mapFst :: (a -> b) -> [(a,c)] -> [(b,c)]
mapFst _ []             = []
mapFst f ((x, y) : xys) = (f x, y) : mapFst f xys

mapSnd :: (a -> b) -> [(c,a)] -> [(c,b)]
mapSnd _ []             = []
mapSnd f ((x, y) : xys) = (x, f y) : mapSnd f xys


------------------------------------------------------------------------------
-- Generalized tuple selectors
------------------------------------------------------------------------------

-- Triples
sel3_1 :: (a, b, c) -> a
sel3_1 (x,_,_) = x
sel3_2 :: (a, b, c) -> b
sel3_2 (_,x,_) = x
sel3_3 :: (a, b, c) -> c
sel3_3 (_,_,x) = x


-- 4-tuples
sel4_1 :: (a, b, c, d) -> a
sel4_1 (x,_,_,_) = x
sel4_2 :: (a, b, c, d) -> b
sel4_2 (_,x,_,_) = x
sel4_3 :: (a, b, c, d) -> c
sel4_3 (_,_,x,_) = x
sel4_4 :: (a, b, c, d) -> d
sel4_4 (_,_,_,x) = x


-- 5-tuples

sel5_1 :: (a, b, c, d, e) -> a
sel5_1 (x,_,_,_,_) = x
sel5_2 :: (a, b, c, d, e) -> b
sel5_2 (_,x,_,_,_) = x
sel5_3 :: (a, b, c, d, e) -> c
sel5_3 (_,_,x,_,_) = x
sel5_4 :: (a, b, c, d, e) -> d
sel5_4 (_,_,_,x,_) = x
sel5_5 :: (a, b, c, d, e) -> e
sel5_5 (_,_,_,_,x) = x


------------------------------------------------------------------------------
-- Floating point utilities
------------------------------------------------------------------------------

-- Floating-point div and modulo operators.

fDiv :: (RealFrac a) => a -> a -> Integer
fDiv x y = fst (fDivMod x y)


fMod :: (RealFrac a) => a -> a -> a
fMod x y = snd (fDivMod x y)


fDivMod :: (RealFrac a) => a -> a -> (Integer, a)
fDivMod x y = (q, r)
    where
        q = (floor (x/y))
        r = x - fromIntegral q * y