# Haskell/Syntactic sugar

*Syntactic sugar* refers to any redundant type of syntax in a programming language that is redundant to the main syntax but which (hopefully) makes the code easier to understand or write.

## Contents

## Functions and constructors[edit]

*For more information, see the chapter More on functions*

description | sweet | unsweet |
---|---|---|

infix operators |
a `mappend` b 1+2 |
mappend a b (+) 1 2 |

sections |
(+2) (3-) |
\x -> x + 2 \x -> 3 - x |

unary minus^{[1]} |
-x |
negate x |

tuples^{[2]} |
(x,y) |
(,) x y |

## Function Bindings[edit]

*For more information, see the chapter Haskell/Variables_and_functions*

description | sweet | unsweet |
---|---|---|

function definitions |
f x y = x * y |
f = \x y -> x * yfurther desugared to f = \x -> \y -> x * y |

pattern matching |
f [] = 0 f (' ':xs) = f xs f (x:xs) = 1 + f xs |
f = \l -> case l of [] -> 0 (' ':xs) -> f xs (x:xs) -> 1 + f xs |

## Lists[edit]

*For more information, see the chapters Lists and tuples, Lists II, Lists III, Understanding monads/List and MonadPlus*

description | sweet | unsweet |
---|---|---|

lists |
[1,2,3] |
1:2:3:[]further desugared to (:) 1 ((:) 2 ((:) 3 [])) |

strings |
"abc" |
['a','b','c']further desugared to 'a':'b':'c':[]even furtherly desugared to (:) 'a' ((:) 'b' ((:) 'c' [])) |

arithmetic sequences |
[1..5] [1,3..9] [1..] [1,3..] |
enumFromTo 1 5 enumFromThenTo 1 3 9 enumFrom 1 enumFromThen 1 3 |

list comprehensions to functions |
[ x | (x,y) <- foos, x < 2 ] |
let ok (x,y) = if x < 2 then [x] else [] in concatMap ok foos |

list comprehensions to list monad functions |
[ x | (x,y) <- foos, x < 2 ] [ (x, bar) | (x,y) <- foos, x < 2, bar <- bars, bar < y ] |
foos >>= \(x, y) -> guard (x < 2) >> return x foos >>= \(x, y) -> guard (x < 2) >> bars >>= \bar -> guard (bar < y) >> return (x, bar) -- or equivalently do (x, y) <- foos guard (x < 2) bar <- bars guard (bar < y) return (x, bar) |

## Records[edit]

description | sweet | unsweet |
---|---|---|

Creation |
data Ball = Ball { x :: Double , y :: Double , radius :: Double , mass :: Double } |
data Ball = Ball Double Double Double Double x :: Ball -> Double x (Ball x_ _ _ _) = x_ y :: Ball -> Double y (Ball _ y_ _ _) = y_ radius :: Ball -> Double radius (Ball _ _ radius_ _) = radius_ mass :: Ball -> Double mass (Ball _ _ _ mass_) = mass_ |

Pattern matching |
getArea Ball {radius = r} = (r**2) * pi |
getArea (Ball _ _ r _) = (r**2) * pi |

Changing values |
moveBall dx dy ball = ball {x = (x ball)+dx, y = (y ball)+dy} |
moveBall dx dy (Ball x y a m) = Ball (x+dx) (y+dy) a m |

## Do notation[edit]

*For more information, see the chapters Understanding monads and do Notation.*

description | sweet | unsweet |
---|---|---|

Sequencing |
do putStrLn "one" putStrLn "two" |
putStrLn "one" >> putStrLn "two" |

Monadic binding |
do x <- getLine putStrLn $ "You typed: " ++ x |
getLine >>= \x -> putStrLn $ "You typed: " ++ x |

Let binding |
do let f xs = xs ++ xs putStrLn $ f "abc" |
let f xs = xs ++ xs in putStrLn $ f "abc" |

Last line |
do x |
x |

## Other constructs[edit]

description | sweet | unsweet |
---|---|---|

if-then-else |
if x then y else z |
case x of True -> y False -> z |

## Literals[edit]

A number (such as 5) in Haskell code is interpreted as `fromInteger 5`

, where the `5`

is an `Integer`

. This allows the literal to be interpreted as `Integer`

, `Int`

, `Float`

etc. Same goes with floating point numbers such as `3.3`

, which are interpreted as `fromRational 3.3`

, where `3.3`

is a `Rational`

. GHC has `OverloadedStrings`

extension, which enables the same behaviour for string types such as `String`

and `ByteString`

varieties from the `Data.ByteString`

modules.

## Type level[edit]

The type `[Int]`

is equivalent to `[] Int`

. This makes it obvious it is an application of `[]`

type constructor (kind `* -> *`

) to `Int`

(kind `*`

).

Analogously, `(Bool, String)`

is equivalent to `(,) Bool String`

, and the same goes with larger tuples.

Function types have the same type of sugar: `Int -> Bool`

can also be written as `(->) Int Bool`

.

## Layout[edit]

*For more information on layout, see the chapter on Indentation*