[GHC] #14569: refutable let bindings produce "irrefutable pattern failed" errors
#14569: refutable let bindings produce "irrefutable pattern failed" errors -------------------------------------+------------------------------------- Reporter: int-e | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.1 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Poor/confusing Unknown/Multiple | error message Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- In ghc-8.2.2 (probably since ghc-8.0.1), strict pattern matches in let bindings produce "Irrefutable pattern failed" errors. {{{#!hs GHCi, version 8.2.2: http://www.haskell.org/ghc/ :? for help Prelude> :set -XBangPatterns Prelude> let ![] = [1] in 1 *** Exception: <interactive>:2:5-13: Irrefutable pattern failed for pattern [] }}} In ghc-7.10.2, normal pattern match failures were produced. {{{#!hs GHCi, version 7.10.2: http://www.haskell.org/ghc/ :? for help Prelude> :set -XBangPatterns Prelude> let ![] = [1] in 1 *** Exception: <interactive>:3:5-13: Non-exhaustive patterns in pattern binding }}} To my mind, the latter error makes much more sense; the effect of the ! is to make the pattern an ordinary, refutable one. Could the old behavior be restored? -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14569 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#14569: refutable let bindings produce "irrefutable pattern failed" errors -------------------------------------+------------------------------------- Reporter: int-e | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Poor/confusing | Unknown/Multiple error message | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by simonpj): I rather agree. Actually even 7.10 had this behaviour. Try {{{ main = let [x] = [] in print (x::Int) }}} and you get the runtime crash (with 7.10) {{{ run: T14569.hs:3:12-19: Irrefutable pattern failed for pattern [x] }}} The real point is: this talk of "irrefutable" patterns is confusing, especially since this one is manifestly refutable. Suggestion: uniformly replace the "Irrefutable pattern failed" message with "Non-exhaustive patterns in pattern binding". To do this * Kill off `Control.Exception.Base.irrefutPatError` * Kill off `MkCore.iRREFUT_PAT_ERROR_ID` and its `Name`, unique, etc. * Use `pAT_ERROR_ID` wherever we currently use `iRREFUT_PAT_ERROR_ID`. Ben, if everyone is happy, would you like to execute on this? -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14569#comment:1 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#14569: refutable let bindings produce "irrefutable pattern failed" errors -------------------------------------+------------------------------------- Reporter: int-e | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Poor/confusing | Unknown/Multiple error message | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by int-e): Replying to [comment:1 simonpj]:
I rather agree. Actually even 7.10 had this behaviour. Try {{{ main = let [x] = [] in print (x::Int) }}} and you get the runtime crash (with 7.10) {{{ run: T14569.hs:3:12-19: Irrefutable pattern failed for pattern [x] }}}
The difference here is that here the pattern is actually (implicitly) irrefutable as per the Haskell 2010 language report. However,
The real point is: this talk of "irrefutable" patterns is confusing, especially since this one is manifestly refutable.
This is a good point, the nomenclature is quite confusing, not just for beginners, but for anyone who isn't intimately familiar with the section on pattern matching in the Haskell report. I wouldn't be sad to see those errors replaced by ordinary incomplete pattern match errors. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14569#comment:2 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#14569: refutable let bindings produce "irrefutable pattern failed" errors -------------------------------------+------------------------------------- Reporter: int-e | Owner: dfeuer Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Poor/confusing | Unknown/Multiple error message | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by dfeuer): * owner: (none) => dfeuer Comment: This sounds like something I can probably manage. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14569#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#14569: refutable let bindings produce "irrefutable pattern failed" errors -------------------------------------+------------------------------------- Reporter: int-e | Owner: dfeuer Type: bug | Status: patch Priority: normal | Milestone: Component: Compiler | Version: 8.2.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Poor/confusing | Unknown/Multiple error message | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Phab:D4261 Wiki Page: | -------------------------------------+------------------------------------- Changes (by dfeuer): * status: new => patch * differential: => Phab:D4261 -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14569#comment:4 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#14569: refutable let bindings produce "irrefutable pattern failed" errors
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Reporter: int-e | Owner: dfeuer
Type: bug | Status: patch
Priority: normal | Milestone:
Component: Compiler | Version: 8.2.1
Resolution: | Keywords:
Operating System: Unknown/Multiple | Architecture:
Type of failure: Poor/confusing | Unknown/Multiple
error message | Test Case:
Blocked By: | Blocking:
Related Tickets: | Differential Rev(s): Phab:D4261
Wiki Page: |
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Comment (by Ben Gamari
#14569: refutable let bindings produce "irrefutable pattern failed" errors -------------------------------------+------------------------------------- Reporter: int-e | Owner: dfeuer Type: bug | Status: closed Priority: normal | Milestone: 8.6.1 Component: Compiler | Version: 8.2.1 Resolution: fixed | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Poor/confusing | Unknown/Multiple error message | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Phab:D4261 Wiki Page: | -------------------------------------+------------------------------------- Changes (by bgamari): * status: patch => closed * resolution: => fixed * milestone: => 8.6.1 -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14569#comment:6 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
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