Function with parameters in Haskell -


i'm trying write few functions have parameters in haskell.

for example: make list kinds of colors, want function color orange list, how specify in function?

getcolor :: -> getcolor = orange

you want function takes list of many colours , returns single colour (presumably of choosing). should start data type represent colours.

data colour = red | orange | yellow | green | blue

now want function getcolour type

getcolour :: colour -> [colour] -> colour

which takes colour , list of colour , picks out desired colour list. however, lists can empty, or list might not contain colour want! getcolour return in case?

in haskell handle function may not return result using maybe. new type of getcolour is

getcolour :: colour -> [colour] -> maybe colour

which means getcolour either return nothing, or just colour colour list.

lastly, i'll mention there few ways write body of getcolour, using pattern matching , explicit recursion, or standard library functions haskell's prelude. assume you're new haskell, i'd recommend former. here's code started:

getcolour _      []     = nothing getcolour colour (x:xs) = ...

is enough write getcolour yourself?


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