Rewrite rules involving LHS lambda?

Edward Kmett ekmett at
Sat Dec 2 20:20:43 UTC 2017

I don't knw of a formal writeup anywhere.

But does that actually mean what you are trying to write?

With the effective placement of "forall" quantifiers on the outside for u
and v I'd assume that x didn't occur in either u or v. Effectively you have
some scope like forall u v. exists x. ...

Under that view, the warnings are accurate, and the rewrite is pretty
purely syntactic.

I don't see how we could write using our current vocabulary that which you

On Sun, Dec 3, 2017 at 4:50 AM, Conal Elliott <conal at> wrote:

> Is there a written explanation and/or examples of rewrite rules involving
> a LHS lambda? Since rule matching is first-order, I'm wondering how terms
> with lambda are matched on the LHS and substituted into on the RHS. For
> instance, I want to restructure a lambda term as follows:
> > foo (\ x -> fmap u v) = bar (\ x -> u) (\ x -> v)
> My intent is that the terms `u` and `v` may contain `x` and that whatever
> variable name is actually used in a term being rewritten is preserved so as
> to re-capture its occurrences on the RHS.
> When I write this sort of rule, I get warnings about `x` being defined but
> not used.
> Thanks,  -- Conal
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> Glasgow-haskell-users mailing list
> Glasgow-haskell-users at
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