CODEWITHSUNDEEP
haskellarguments
Daniel
Daniel

Reputation: 541

Haskell: Equation as argument in a function

Is there any way I can make a function that takes a mathematical equation as an argument? For example

derive :: --equation
...
main = print (derive $ x**2-x)

Would I need to make a custom data type?

Upvotes: 0

Views: 166

Answers (1)

chepner
chepner

Reputation: 531625

Yes; you need to create a data type that represents a formula, rather than passing a Haskell expression that needs to be evaluated. For example,

data Formula = Term Int Int   -- coefficient and exponent
             | Sum Formula Formula deriving Show

derive :: Formula -> Formula
derive (Term coeff exp) = Term (coeff * exp) (exp - 1)
derive (Sum x y) = Sum (derive x) (derive y)

main = print (derive $ Sum (Term 1 2) (Term (-1) 1))

Upvotes: 3

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