2009/6/22 Malcolm Wallace <malcolm.wall...@cs.york.ac.uk>: > Erik de Castro Lopo <mle...@mega-nerd.com> wrote: > >> Vasili I. Galchin wrote: >> >> > "where/let" functions use the >> > same name for function parameters as the outer function and hence >> > there is a "shadow" warning from the compiler. >> >> In Haskell there is an easy way around this. Variables can >> be name a, a', a'' and so on. ... >> ... its a good idea to fix these warnings. > > I would _strongly_ advise not to do that. By trying to silence the > spurious warning about shadowing, there is enormous potential to > introduce new bugs that were not there before. > > Example: > > f a b = g (a+b) (b-a) > where g a c = a*c > > ghc warns that g's parameter a shadows the parameter to f. So we > introduce a primed identifier to eliminate the warning: > > f a b = g (a+b) (b-a) > where g a' c = a*c > > Now, no warnings! But, oops, this function does not do the same thing. > We forgot to add a prime to all occurrences of a on the right-hand-side. > > Particularly in larger examples, it can be remarkably easy to miss an > occurrence of the variable whose name you are refactoring. The key > point is that in this situation, unlike most refactorings, the compiler > _cannot_ help you find the mistake with useful error messages or > warnings.
What about an editor (or emacs mode or…) that support variable renaming? Maybe there is already one? Loup _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
