#14875: -ddump-splices pretty-printing oddities with case statements
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Reporter: RyanGlScott | Owner: (none)
Type: bug | Status: closed
Priority: normal | Milestone: 8.6.1
Component: Compiler | Version: 8.2.2
Resolution: fixed | Keywords:
Operating System: Unknown/Multiple | Architecture:
Type of failure: Debugging | Unknown/Multiple
information is incorrect | Test Case:
Blocked By: | Blocking:
Related Tickets: | Differential Rev(s): Phab:D4688
Wiki Page: |
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Comment (by Ben Gamari ):
In [changeset:"21e1a00c0ccf3072ccc04cd1acfc541c141189d2/ghc"
21e1a00c/ghc]:
{{{
#!CommitTicketReference repository="ghc"
revision="21e1a00c0ccf3072ccc04cd1acfc541c141189d2"
Fix #14875 by introducing PprPrec, and using it
Trying to determine when to insert parentheses during TH
conversion is a bit of a mess. There is an assortment of functions
that try to detect this, such as:
* `hsExprNeedsParens`
* `isCompoundHsType`
* `hsPatNeedsParens`
* `isCompoundPat`
* etc.
To make things worse, each of them have slightly different semantics.
Plus, they don't work well in the presence of explicit type
signatures, as #14875 demonstrates.
All of these problems can be alleviated with the use of an explicit
precedence argument (much like what `showsPrec` currently does). To
accomplish this, I introduce a new `PprPrec` data type, and define
standard predences for things like function application, infix
operators, function arrows, and explicit type signatures (that last
one is new). I then added `PprPrec` arguments to the various
`-NeedsParens` functions, and use them to make smarter decisions
about when things need to be parenthesized.
A nice side effect is that functions like `isCompoundHsType` are
now completely unneeded, since they're simply aliases for
`hsTypeNeedsParens appPrec`. As a result, I did a bit of refactoring
to remove these sorts of functions. I also did a pass over various
utility functions in GHC for constructing AST forms and used more
appropriate precedences where convenient.
Along the way, I also ripped out the existing `TyPrec`
data type (which was tailor-made for pretty-printing `Type`s) and
replaced it with `PprPrec` for consistency.
Test Plan: make test TEST=T14875
Reviewers: alanz, goldfire, bgamari
Reviewed By: bgamari
Subscribers: rwbarton, thomie, carter
GHC Trac Issues: #14875
Differential Revision: https://phabricator.haskell.org/D4688
}}}
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Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14875#comment:9
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