[Haskell-cafe] Substituting values

[Petr P]

Hi Alvaro,

I think you need something wha Scala has - the ability to create a partial
function from a case expression. In Scala you could write

  def update[A](f: PartialFunction[A,A])(v: A): A =
    f.orElse({ case x => x } : PartialFunction[A,A]).apply(v);

and then use it like

  update[Int]({ case Foo => Bar })

But AFAIK there is nothing like this in Haskell. Maybe separating 'of' from
'case' would be the way to extend Haskell with such a feature <
http://www.haskell.org/pipermail/haskell-cafe/2012-November/104884.html>

Best regards,
Petr



2012/12/21 Radical <radical at google.com>

> Sometimes I'll need something like:
>
>   if value == Foo then Bar else value
>
> Or some syntactic variation thereof:
>
>   case value of { Foo -> Bar; _ -> value }
>
> Is there a better/shorter way to do it? I'm surprised that it's more
> complicated to substitute a value on its own than e.g. in a list, using
> filter. Or perhaps I'm missing the right abstraction?
>
> Thanks,
>
> Alvaro
>
>
>
>
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