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haskellseq

`seq` on partially applied functions

Lets say I have the following:

f :: a -> b -> c
g :: b -> c
g = f 10

Now lets say f is actually:

f x y = f1 x + y

Would:

g `seq` ...

actually evaluate f1 10, so later when running

g 9

it's actually just a simple addition?

If not, is there a way to "evaluate" parts of a partially applied function?

I'm looking for a generic solution, one that doesn't depend on knowing how f and g work.

Solution

  • seq is shallow:

    Prelude> let f1 = undefined
Prelude> let f = \x -> \y -> f1 x + y
Prelude> let g = f 10
Prelude> g `seq` 1
1
Prelude> g 9
*** Exception: Prelude.undefined
Prelude>

    I'd take a look at Control.DeepSeq: http://hackage.haskell.org/packages/archive/deepseq/1.2.0.1/doc/html/Control-DeepSeq.html