[Haskell-cafe] Mapping a list of functions

Gregory Collins greg at gregorycollins.net
Thu Jun 17 15:19:55 EDT 2010

Martin Drautzburg <Martin.Drautzburg at web.de> writes:

> Hello all
> The standard map function applies a single function to a list of arguments. 
> But what if I want to apply a list of functions to a single argument. I can 
> of course write such a function, but I wonder if there is a standard way of 
> doing this,

    > (map ($ 3) [(+2), (*4), (/3)])::[Double]

> Related to that is the problem, that the function in map may require more than 
> one argument, so I need to apply it partially to some value(s) first. But 
> what if I want to fix its second and third argument and not its first 
> argument? Can flip help?

The "pointfree" command-line tool can help you find good short forms for
this kind of thing:

    $ pointfree '\x -> f x 2 3'
    flip (flip f 2) 3

In this case the explicit (pointed) lambda is simpler so I would usually
just use that.

Gregory Collins <greg at gregorycollins.net>

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