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Stumped with composition
f#

This is probably a silly question, but I'm new to F#...

I have two functions:

val _evalSH2 : float * float -> float

val _cartToSph : float -> float -> float -> float * float

Perhaps this is an error in judgement, but I assumed I would be able to compose this functions as so:

_cartToSph >> _evalSH2

However, I get the error when I try to do so.

_cartToSph >> _evalSH2

--------------^^^^^^^^^

stdin(3,15): error FS0001: Type mismatch. Expecting a

(float -> float -> float * float) -> 'a

but given a

float * float -> float.

The type 'float -> float -> float * float' does not match the type 'float * float'.

Any help would be much appreciated, thanks.

.

It's a good question.

I think the issue is that (>>) only works with a single (curried) argument - it can't look ahead to see that multiple applications on the left-hand argument will eventually yield the right return type. The code below illustrates this and suggest a solution.

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let f(x,y) = x + y + 1.0
let g (x:float) (y:float) (z:float) = (x,y)

f (g 1.0 1.0 1.0) |> printfn "%f"

// (g >> f) 1.0 1.0 1.0 |> printfn "%f" // no
(g 1.0 1.0 >> f) 1.0 |> printfn "%f" // yes
(fun x y -> (g x y >> f)) 1.0 1.0 1.0 |> printfn "%f" // what you want?
By on 10/12/2008 12:15 PM ()

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