What is the Haskell idiom for "if then else if then"
I've just written this piece of code if r < 0 then LEFT else if r > 0 then RIGHT else STRAIGHT which works just fine but it does look rather clunky (as it would in any language I suppose). Is there a Haskell idiom for this type of code?
Am Montag 30 März 2009 17:33:02 schrieb Peter Hickman:
I've just written this piece of code
if r < 0 then LEFT else if r > 0 then RIGHT else STRAIGHT
which works just fine but it does look rather clunky (as it would in any language I suppose). Is there a Haskell idiom for this type of code?
Usually, people use guards: function r | r < 0 = LEFT | r > 0 = RIGHT | otherwise = STRAIGHT Another option would be a case: case compare r 0 of LT -> LEFT GT -> RIGHT EQ -> STRAIGHT You can also have a case with guards: case expression of pattern1 | condition1.1 -> result1.1 | condition1.2 -> result1.2 pattern2 | condition2.1 -> result2.1 pattern3 -> result3 _ -> defaultresult
That works, but I guess a case statement would be nicer: case compare r 0 of LT -> LEFT GT -> RIGHT EQ -> STRAIGHT This uses the compare function, which results in a value of the Ordering datatype, which consists of the constructors LT, EQ and GT. Peter Hickman wrote:
I've just written this piece of code
if r < 0 then LEFT else if r > 0 then RIGHT else STRAIGHT
which works just fine but it does look rather clunky (as it would in any language I suppose). Is there a Haskell idiom for this type of code?
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http://www.haskell.org/haskellwiki/If-then-else#Replace_syntactic_sugar_by_a...
mentions that there is no such function in Prelude.
On Mon, Mar 30, 2009 at 11:33 AM, Peter Hickman
I've just written this piece of code
if r < 0 then LEFT else if r > 0 then RIGHT else STRAIGHT
which works just fine but it does look rather clunky (as it would in any language I suppose). Is there a Haskell idiom for this type of code?
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Peter Hickman