NoMonomorphismRestriction

[Isaac Dupree]

> The paper makes the (somewhat radical) case for not generalising local bindings at all; which would at a stroke remove most of the issues of the MR.  (We'd still need to think about the top level.)
> 
> We'd love to know what any of you think of the idea.

I read the paper (except section 5 which is very technical).

I like that it makes
(let x = ... in ...)
behave the same as
(\x -> ...) (...)
. Understanding how to respond to type inference and error messages is 
hard enough without having additional differences in innocent-looking 
code.  Do you think my hope is reasonable that not-generalizing could 
lead to better error messages?  I don't quite understand the issues[*], 
but I suspect that not-generalizing would at least make *me* less 
confused when fixing error messages because there are fewer different 
typechecker behaviors to think about.  I guess it's still possible to 
use explicit type-signatures to make let-bindings polymorphic, in a way 
that is difficult or impossible for lambda or case? (I guess for lambda, 
it would require making the lambda into a rank-2 function, though I'm 
not sure how to do that syntactically.)

[*] e.g., the gmapT / rank-2 example confuses me; would it work if 
(...blah...) were passed directly to gmapT without the let?

Also, does it happen to solve the 2^n worst-case typechecking?

-Isaac