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

[Jonas Almström Duregård]

Hi,

> if param1
>    then sp = f1 . f2 . f3
>    else sp = f1 . f3

If you have many situations like these, i.e. where one or several
components are conditional, you can define a function

when True  f = f
when False _ = id

And now you can define sp like this:

sp = f1 . when param1 f2 . f3

Regards,
Jonas

On 24 August 2011 14:35, 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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