[Haskell-cafe] Re: Seeking advice about monadic traversal functions

[Martijn van Steenbergen]

On 3/31/10 12:44, Heinrich Apfelmus wrote:
>          go Next (Single x t1) = liftM (Single x) (rewrite f t1)
>          go Next (Fork t1 t2 ) = liftM2 Fork (rewrite f t1)
>                                              (rewrite f t2)
>
> In particular,  liftM  and  liftM2  make it apparent that we're just
> wrapping the result in a constructor.

A small remark: I prefer using applicative notation for this:

> go Next (Single x t1) = Single x <$> rewrite f t1
> go Next (Fork t1 t2 ) = Fork     <$> rewrite f t1 <*> rewrite f t2

Martijn.