Opened 5 years ago

Closed 4 years ago

Last modified 4 years ago

#9618 closed bug (duplicate)

Undocument ImpredicativeTypes

Reported by: dfeuer Owned by:
Priority: normal Milestone: 8.0.1
Component: Documentation Version: 7.8.3
Keywords: Cc:
Operating System: Unknown/Multiple Architecture: Unknown/Multiple
Type of failure: Documentation bug Test Case:
Blocked By: Blocking:
Related Tickets: #8808 Differential Rev(s):
Wiki Page:

Description (last modified by dfeuer)

I understand that Simon Peyton Jones intends to make ImpredicativeTypes work some day, but it doesn't work now. I think the thing to do for now is to remove it from the user manual. It can be put back in later if and when it's fixed.

Change History (6)

comment:1 Changed 5 years ago by dfeuer

Description: modified (diff)
Milestone: 7.10.1
Type of failure: None/UnknownDocumentation bug

comment:2 Changed 5 years ago by thomie

Perhaps never showing the following suggestion either, see compiler/typecheck/TcErrors.lhs:

Perhaps you want ImpredicativeTypes

comment:3 Changed 5 years ago by goldfire

I'm not convinced ImpredicativeTypes should be removed from the manual. Sometimes[citation needed] I have needed ImpredicativeTypes to get my code to type check. ImpredicativeTypes isn't wrong -- it's just very, very rough around the edges. It won't (as far as I know) cause your code to segfault or otherwise go astray. The extension just doesn't work in all the contexts we might like it to.

So, instead of removing it altogether, I think we should label it as experimental and very limited.

That all said, I don't feel terribly strongly about this and am happy enough if the majority disagrees with me here.

comment:4 Changed 5 years ago by thoughtpolice

Milestone: 7.10.17.12.1

Moving to 7.12.1 milestone; if you feel this is an error and should be addressed sooner, please move it back to the 7.10.1 milestone.

comment:5 Changed 4 years ago by thomie

Resolution: duplicate
Status: newclosed

In #10325, SPJ updated the User's guide and the error message: "GHC doesn't yet support impredicative polymorphism".

comment:6 Changed 4 years ago by thoughtpolice

Milestone: 7.12.18.0.1

Milestone renamed

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