[Haskell-cafe] Function composition in run-time?

[Arseniy Alekseyev]

If your functions have the same type, then you can easily collect them
in a data structure, say list, and fold that.

For example:

function :: String -> (String -> String)
function "f1" = f1
function "f2" = f2
function "f3" = f3

runAUserSpecifiedComposition :: String -> F
runAUserSpecifiedComposition = foldl (.) id . map function . words

runAUserSpecifiedComposition "f1 f2 f3" should be equal to (f1 . f2 . f3) now.

On 24 August 2011 13:35, dokondr <dokondr at gmail.com> wrote:
> Hi,
> What is the Haskell way to compose functions in run-time?
> Depending on configuration parameters I need to be able to compose function
> in several ways without recompilation.
> When program starts it reads configuration parameters from a text file. For
> example, I have three functions, f1, f2, f3,  each doing some string
> processing. I need to support two configurations of string processors :
>
> if param1
>    then sp = f1 . f2 . f3
>    else sp = f1 . f3
>
> I'd like to avoid 'if' somehow and instead use some declarative way to
> specify code to run in external configuration file. In other words I need
> some easy tools to create mini DSLs without all the efforts usually involved
> with implementing full-blown DSL.
>
> Thanks,
> Dmitri
>
>
>
>
>
>
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