#16096: let x = ... and x = ... are not the same in GHCi -------------------------------------+------------------------------------- Reporter: osa1 | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: GHCi | Version: 8.6.3 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Description changed by osa1: Old description:
With #7253 we implemented support for `x = ...` in GHCi which is supposed to do the same thing as `let x = ...`, but they're currently different, as observed in #16089, #15721, and probably in other tickets. Here's a reproducer:
{{{ ~ $ ghci -ddump-bcos GHCi, version 8.4.4: http://www.haskell.org/ghc/ :? for help
...
λ:1> let x = [True,False]
==================== Proto-BCOs ==================== ProtoBCO ExprTopLevel_E0#0 []: let sat_s1vF = ... in ... bitmap: 0 [] PUSH_G GHC.Types.[] PUSH_G GHC.Types.False PACK : 2 PUSH_L 0 PUSH_G GHC.Types.True PACK : 2 PUSH_G GHC.Types.[] PUSH_L 1 PACK : 2 PUSH_L 0 PUSH_APPLY_P PUSH_G GHC.Base.returnIO SLIDE 3 3 ENTER
λ:2> x = [True,False]
==================== Proto-BCOs ==================== ProtoBCO x1_r1wJ#0 []: GHC.Types.: @ GHC.Types.Bool GHC.Types.False (GHC.Types.[] @ GHC.Types.Bool) bitmap: 0 [] PUSH_G GHC.Types.[] PUSH_G GHC.Types.False PACK : 2 ENTER
ProtoBCO Ghci2.x#0 []: GHC.Types.: @ GHC.Types.Bool GHC.Types.True x1_r1wJ bitmap: 0 [] PUSH_G x1_r1wJ PUSH_G GHC.Types.True PACK : 2 ENTER
... }}}
Expected behavior: these two should generate the same byte code, and should be subject to same checks (e.g. for shadowing).
New description: With #7253 we implemented support for `x = ...` in GHCi which is supposed to do the same thing as `let x = ...`, but they're currently different, as observed in #16089, #15721, and probably in other tickets. Here's a reproducer: {{{ ~ $ ghci -ddump-bcos GHCi, version 8.4.4: http://www.haskell.org/ghc/ :? for help ... λ:1> let x = [True,False] ==================== Proto-BCOs ==================== ProtoBCO ExprTopLevel_E0#0 []: let sat_s1vF = ... in ... bitmap: 0 [] PUSH_G GHC.Types.[] PUSH_G GHC.Types.False PACK : 2 PUSH_L 0 PUSH_G GHC.Types.True PACK : 2 PUSH_G GHC.Types.[] PUSH_L 1 PACK : 2 PUSH_L 0 PUSH_APPLY_P PUSH_G GHC.Base.returnIO SLIDE 3 3 ENTER λ:2> x = [True,False] ==================== Proto-BCOs ==================== ProtoBCO x1_r1wJ#0 []: GHC.Types.: @ GHC.Types.Bool GHC.Types.False (GHC.Types.[] @ GHC.Types.Bool) bitmap: 0 [] PUSH_G GHC.Types.[] PUSH_G GHC.Types.False PACK : 2 ENTER ProtoBCO Ghci2.x#0 []: GHC.Types.: @ GHC.Types.Bool GHC.Types.True x1_r1wJ bitmap: 0 [] PUSH_G x1_r1wJ PUSH_G GHC.Types.True PACK : 2 ENTER ... }}} Expected behavior: these two should generate the same byte code, and should be subject to same checks (e.g. for shadowing). (Example above uses 8.4.4, but this can be reproduced with GHC HEAD too) -- -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/16096#comment:1 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler