[Haskell-cafe] Solved but strange error in type inference

Yucheng Zhang yczhang89 at gmail.com
Tue Jan 3 18:01:27 CET 2012

On Wed, Jan 4, 2012 at 12:44 AM, Yves Parès <limestrael at gmail.com> wrote:
> Remove subsome type signature. You are redeclaring type variables which
> obviously cannot match those of legSome.
> This cannot work without scoped type variables (and ad-hoc foralls to bring
> them to scope, of course).

That subsome type signature is from the original code.

I wonder why the redeclared type variables cannot match those of legSome?

p.s. I just realized that my changed code missed the line:

> import qualified Data.Map as M

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