#7861: deferred type error with rankNTypes
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Reporter: guest | Owner:
Type: bug | Status: closed
Priority: normal | Milestone:
Component: Compiler | Version: 7.6.2
Resolution: wontfix | Keywords:
Operating System: Linux | Architecture: x86_64 (amd64)
Type of failure: Compile-time | Test Case:
crash | typecheck/should_run/T7861
Blocked By: | Blocking:
Related Tickets: |
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Comment (by Ben Gamari ):
In [changeset:"4c96e7cf56fc67ad09efaf8c5de1c8d7a0f5cedd/ghc"
4c96e7cf/ghc]:
{{{
#!CommitTicketReference repository="ghc"
revision="4c96e7cf56fc67ad09efaf8c5de1c8d7a0f5cedd"
Testsuite: add ImpredicativeTypes to T7861 (#7861)
The test was failing with:
T7861: T7861.hs:15:13:
Cannot instantiate unification variable ‘t0’
with a type involving foralls: A a0 -> a0
GHC doesn't yet support impredicative polymorphism
In the first argument of ‘seq’, namely ‘f’
In a stmt of a 'do' block: f `seq` print "Hello 2"
It requires ImpredicativeTypes, at least since 7.8, because we
instantiate seq's type (c->d->d) with f's type (c:= (forall b. a) -> a),
which is polymorphic (it has foralls).
I simplified the test a bit by removing the type synonym, and verified
that ghc-7.6.3 still panics on this test.
Reviewers: simonpj, austin, bgamari
Reviewed By: bgamari
Subscribers: thomie
Differential Revision: https://phabricator.haskell.org/D1080
GHC Trac Issues: #7861
}}}
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Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/7861#comment:5
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