CODEWITHSUNDEEP
haskellfunctional-programming
OneMoreError
OneMoreError

Reputation: 7728

Understanding currying by example

I was reading about curried function somewhere, which sounded confusing. The example confused me even further. Lets say I have a function:

power :: (Int, Float) -> Float -- computes the nth power of b
power (n, b) =
    if n == 0 then 1.0 else b * power (n-1, b)

Now I define another function powerc:: Int -> Float -> Float such that

powerc n b =
    if n == 0 then 1.0 else b * powerc (n-1) b

Can someone please explain to me how is powerc a curried version of power function.

Upvotes: 0

Views: 448

Answers (2)

AshleyF
AshleyF

Reputation: 3742

The former is a function taking an Int, Float tuple, while the latter is essentially a chain of functions each taking a single argument and returning a function taking the next.

That is, powerc takes an Int and returns a function that takes a Float and returns a Float.

You could make use of this with partial application. For example square = powerc 2 or cube = powerc 3 which are each then simple Float -> Float functions with the value for n captured.

Non-curried functions don't afford this easy partial application. It's nice to use partial application when the leading arguments are a kind of one-time configuration of the function's behavior. It also becomes particularly useful when trying to reshape functions to be passed to higher-order functions. For example, you could map powerc 2 (without defining) over a list to square them all.

Hope that helps!

Upvotes: 5

Cfr
Cfr

Reputation: 5133

Because powerc allows partial application now:

square = powerc 2

BTW,

powerc = curry power

Upvotes: 5

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