I forget whether I've aired this on the list, but I'm seriously thinking that we should change 'forall' to 'exists' in existential data constructors like this one. One has to explain 'forall' every time. But we'd lose a keyword.
"exists" (like "forall" in ghc only) could be used independently in a type or expression context without loosing something.
Earlier explanations of "forall" as a sort of "negated exists" become plain wrong when now "exists" should replace "forall" at the very same position. Is moving the keyword exists up an option (and be backward compatible)?
Or omit the keyword altogether (Doaitse has suggested this before). This is quite in line with uses of quantifiers elsewhere (in the horn rule `path(A,C) :- path(A,B), path(B, C)' the variable `C' is implicitly existentially quantified in the body).
(you mean `B' is implicitly existentially quantified?!)
Omitting the keyword may lead to unintended existential quantification
and should be accompanied with a noticable warning (that may be switched off by experts).
Haskell should support both implicit (with warning) and explicit existential (and universal) quantification!
Christian
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