[Haskell-cafe] Re: Debugging partial functions by the rules

Jacques Carette carette at mcmaster.ca
Wed Nov 15 13:08:55 EST 2006

Robert Dockins wrote:
> Or how about.... ??
> lookupVarible target env =
>    case [ v | (n,v) <- env, n==target ] of
>       (x:_) -> x
>       _ -> assert False $ "BUG: Unexpected variable out of scope 
> "++(show target)++" in environment "++(show env)
Other have pointed out that, in the CURRENT Haskell semantics, the above 
is quite difficult to reason about.

Note that the whole point of Wolfram Kahl's Pattern Matching Calculus is 
to restore equational reasoning to pattern-matches.


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