> >>Just a little remark on the side: 'If' and 'case' demand exactly one > >>expression. In such cases allowing zero expressions is not a > >>generalization but an unnecessary complication. 'Let' and 'where' > >>allow any number of bindings, so allowing zero bindings (instead of > >>demanding at least one) is a simplification. > > > >I meant the branches of a case (the report specifies at least 1). > > I think it's important to keep some possibility for the compiler to detect > probable errors as syntax errors. If all syntax is inhabited by strange > defaults then this just means simple errors will go undetected eg: > > let a = case foo of > > Here, the user has probably got sidetracked into editing some other part of > the program and just forgotten to get back to fill in the cases for the > case construct. Allowing zero cases means the user will get a strange > runtime error instead as the "function" part of the case is undefined.
I agree. On the other hand, if there are uninhabited types (modulo _|_), it might be nice to have an empty case as an explicit eliminator. > let z = \y (foo y) > > Here, it seems clear that the user has just forgotten to type the -> which > means a simple syntax error would get transformed into a much more puzzling > (esp for a newbie) type error. Again, for the lambda I obviously meant the case of 0 variables, i.e. something like (\ -> y) which would then just be equivalent to y. I think this case is probably the one that's most comparable to the situation in question (whether to allow empty forall's). Since the designers of previous Haskell versions obviously thought it's a good idea to disallow empty lambdas, let's disallow empty forall's as well. Cheers, Andres _______________________________________________ Haskell-prime mailing list Haskell-prime@haskell.org http://www.haskell.org/mailman/listinfo/haskell-prime
