[Haskell-cafe] Re: Combining Wouter's expressions with extensible records

Ron Alford ronwalf at volus.net
Thu Jul 10 23:20:56 EDT 2008

Ok, I'm closer, but I'm running into a problem with typeOf and lists,
of all things:
*WouterTest> typeOf (eVar "v" :: TermExpr)
Planning.Wouter.Expr (Planning.Wouter.:+: WouterTest.Const WouterTest.Var)
*WouterTest> typeOf ([eVar "v"] :: [TermExpr])
*** Exception: Prelude.undefined

I'm pretty sure this is the culprit for getName:
*WouterTest> getName testNamed
"*** Exception: Prelude.undefined

Any hints?

Also, anyone have hints for how to get automatic derivation of Data (Expr f) ?
I don't want to proliferate the last lines:
deriving instance Data (Expr (And :+: Atomic (Expr (Const :+: Var))))
deriving instance Data (Expr (Const :+: Var))

-Ron Alford
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