[Haskell-cafe] Simple Table Update

[Ryan Ingram]

On Wed, Oct 8, 2008 at 9:12 PM, Paul Keir <pkeir at dcs.gla.ac.uk> wrote:
> It brings tears to my eyes to see such a beautiful function ;) You've hit
> the nail on the head Ryan. The new version of my second previous code
> snippet now no longer requires "fixpu*", and is:
>
> typeCheckAST (Program pus) = Program $ snd $ mapAccumL f [] pus
>
>   where f st pu = (st ++ [("",[])],pu)

I'm confused about this.  If I'm reading this correctly,

    snd $ mapAccumL f (undefined) pus == map id pus == pus

  -- ryan