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The Happy parser generator for Haskell
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happy fails to generate valid Haskell when `<$>` is used. #115

Open vmchale opened 6 years ago

vmchale commented 6 years ago

The bug in question came from a parser hosted here. In short, if you write

| FunName Universals OptTermetric OptType OptExpression { PreF $1 (fst <$> $4) [] $2 [NoArgs] (snd <$> $4) $3 $5 }

instead of

| FunName Universals OptTermetric OptType OptExpression { PreF $1 (fmap fst $4) [] $2 [NoArgs] (fmap snd $4) $3 $5 }

it will fail during compilation with an arcane error message, viz.

/home/vanessa/programming/haskell/done/ats/dist-newstyle/build/x86_64-linux/ghc-8.2.2/language-ats-1.0.1.0/opt/build/Language/ATS/Parser.hs:4832:38: error:
    • Couldn't match type ‘Maybe (String, Type AlexPosn)
                           -> (b0, b0) -> b0’
                     with ‘Maybe (Expression AlexPosn)’
      Expected type: HappyStk
                       (HappyAbsSyn
                          (ATS AlexPosn)
                          [Declaration AlexPosn]
                          [Type AlexPosn]
                          [Type AlexPosn]
                          (Type AlexPosn)
                          [Arg AlexPosn]
                          [Arg AlexPosn]
                          (Arg AlexPosn)
                          (Arg AlexPosn)
                          (Expression AlexPosn)
                          [Pattern AlexPosn]
                          (Pattern AlexPosn)
                          [(Pattern AlexPosn, LambdaType AlexPosn, Expression AlexPosn)]
                          [(Expression AlexPosn, LambdaType AlexPosn, Expression AlexPosn)]
                          (Maybe [Expression AlexPosn], [Expression AlexPosn])
                          [Expression AlexPosn]
                          [Expression AlexPosn]
                          (LambdaType AlexPosn)
                          (LambdaType AlexPosn)
                          (Expression AlexPosn)
                          [Type AlexPosn]
                          (Expression AlexPosn)
                          [StaticExpression AlexPosn]
                          [Declaration AlexPosn]
                          (StaticExpression AlexPosn)
                          (Expression AlexPosn)
                          (AlexPosn, StaticExpression AlexPosn)
                          (Sort AlexPosn)
                          [String]
                          (Existential AlexPosn)
                          [StaticExpression AlexPosn]
                          (Universal AlexPosn)
                          [[Type AlexPosn]]
                          [[Type AlexPosn]]
                          (Either (StaticExpression AlexPosn) (Expression AlexPosn))
                          (Implementation AlexPosn)
                          (Implementation AlexPosn)
                          (Name AlexPosn)
                          (Name AlexPosn)
                          [(String, Expression AlexPosn)]
                          [(String, Type AlexPosn)]
                          [String]
                          (Maybe (Type AlexPosn))
                          [StaticExpression AlexPosn]
                          (Leaf AlexPosn)
                          [Leaf AlexPosn]
                          [Universal AlexPosn]
                          (Maybe (StaticExpression AlexPosn))
                          (UnOp AlexPosn)
                          (BinOp AlexPosn)
                          (Maybe (Expression AlexPosn))
                          (DataPropLeaf AlexPosn)
                          [DataPropLeaf AlexPosn]
                          String
                          (Maybe (String, Type AlexPosn))
                          (PreFunction AlexPosn)
                          (Declaration AlexPosn)
                          (Declaration AlexPosn)
                          (Declaration AlexPosn)
                          [Declaration AlexPosn]
                          String
                          (Maybe (Type AlexPosn))
                          [Arg AlexPosn]
                          [SortArg AlexPosn]
                          (Maybe [SortArg AlexPosn])
                          (Declaration AlexPosn)
                          (Fixity AlexPosn)
                          String
                          [String]
                          (StackFunction AlexPosn)
                          [Declaration AlexPosn]
                          (Declaration AlexPosn)
                          (DataSortLeaf AlexPosn)
                          [DataSortLeaf AlexPosn]
                          (Declaration AlexPosn)
                          (Declaration AlexPosn)
                          (Declaration AlexPosn))
                     -> HappyStk
                          (HappyAbsSyn
                             (ATS AlexPosn)
                             [Declaration AlexPosn]
                             [Type AlexPosn]
                             [Type AlexPosn]
                             (Type AlexPosn)
                             [Arg AlexPosn]
                             [Arg AlexPosn]
                             (Arg AlexPosn)
                             (Arg AlexPosn)
                             (Expression AlexPosn)
                             [Pattern AlexPosn]
                             (Pattern AlexPosn)
                             [(Pattern AlexPosn, LambdaType AlexPosn, Expression AlexPosn)]
                             [(Expression AlexPosn, LambdaType AlexPosn, Expression AlexPosn)]
                             (Maybe [Expression AlexPosn], [Expression AlexPosn])
                             [Expression AlexPosn]
                             [Expression AlexPosn]
                             (LambdaType AlexPosn)
                             (LambdaType AlexPosn)
                             (Expression AlexPosn)
                             [Type AlexPosn]
                             (Expression AlexPosn)
                             [StaticExpression AlexPosn]
                             [Declaration AlexPosn]
                             (StaticExpression AlexPosn)
                             (Expression AlexPosn)
                             (AlexPosn, StaticExpression AlexPosn)
                             (Sort AlexPosn)
                             [String]
                             (Existential AlexPosn)
                             [StaticExpression AlexPosn]
                             (Universal AlexPosn)
                             [[Type AlexPosn]]
                             [[Type AlexPosn]]
                             (Either (StaticExpression AlexPosn) (Expression AlexPosn))
                             (Implementation AlexPosn)
                             (Implementation AlexPosn)
                             (Name AlexPosn)
                             (Name AlexPosn)
                             [(String, Expression AlexPosn)]
                             [(String, Type AlexPosn)]
                             [String]
                             (Maybe (Type AlexPosn))
                             [StaticExpression AlexPosn]
                             (Leaf AlexPosn)
                             [Leaf AlexPosn]
                             [Universal AlexPosn]
                             (Maybe (StaticExpression AlexPosn))
                             (UnOp AlexPosn)
                             (BinOp AlexPosn)
                             (Maybe (Expression AlexPosn))
                             (DataPropLeaf AlexPosn)
                             [DataPropLeaf AlexPosn]
                             String
                             (Maybe (String, Type AlexPosn))
                             (PreFunction AlexPosn)
                             (Declaration AlexPosn)
                             (Declaration AlexPosn)
                             (Declaration AlexPosn)
                             [Declaration AlexPosn]
                             String
                             (Maybe (Type AlexPosn))
                             [Arg AlexPosn]
                             [SortArg AlexPosn]
                             (Maybe [SortArg AlexPosn])
                             (Declaration AlexPosn)
                             (Fixity AlexPosn)
                             String
                             [String]
                             (StackFunction AlexPosn)
                             [Declaration AlexPosn]
                             (Declaration AlexPosn)
                             (DataSortLeaf AlexPosn)
                             [DataSortLeaf AlexPosn]
                             (Declaration AlexPosn)
                             (Declaration AlexPosn)
                             (Declaration AlexPosn))
        Actual type: HappyStk
                       (HappyAbsSyn
                          (ATS AlexPosn)
                          [Declaration AlexPosn]
                          [Type AlexPosn]
                          [Type AlexPosn]
                          (Type AlexPosn)
                          [Arg AlexPosn]
                          [Arg AlexPosn]
                          (Arg AlexPosn)
                          (Arg AlexPosn)
                          (Expression AlexPosn)
                          [Pattern AlexPosn]
                          (Pattern AlexPosn)
                          [(Pattern AlexPosn, LambdaType AlexPosn, Expression AlexPosn)]
                          [(Expression AlexPosn, LambdaType AlexPosn, Expression AlexPosn)]
                          (Maybe [Expression AlexPosn], [Expression AlexPosn])
                          [Expression AlexPosn]
                          [Expression AlexPosn]
                          (LambdaType AlexPosn)
                          (LambdaType AlexPosn)
                          (Expression AlexPosn)
                          [Type AlexPosn]
                          (Expression AlexPosn)
                          [StaticExpression AlexPosn]
                          [Declaration AlexPosn]
                          (StaticExpression AlexPosn)
                          (Expression AlexPosn)
                          (AlexPosn, StaticExpression AlexPosn)
                          (Sort AlexPosn)
                          [String]
                          (Existential AlexPosn)
                          [StaticExpression AlexPosn]
                          (Universal AlexPosn)
                          [[Type AlexPosn]]
                          [[Type AlexPosn]]
                          (Either (StaticExpression AlexPosn) (Expression AlexPosn))
                          (Implementation AlexPosn)
                          (Implementation AlexPosn)
                          (Name AlexPosn)
                          (Name AlexPosn)
                          [(String, Expression AlexPosn)]
                          [(String, Type AlexPosn)]
                          [String]
                          (Maybe (Type AlexPosn))
                          [StaticExpression AlexPosn]
                          (Leaf AlexPosn)
                          [Leaf AlexPosn]
                          [Universal AlexPosn]
                          (Maybe (StaticExpression AlexPosn))
                          (UnOp AlexPosn)
                          (BinOp AlexPosn)
                          (Maybe (String, Type AlexPosn) -> (b0, b0) -> b0)
                          (DataPropLeaf AlexPosn)
                          [DataPropLeaf AlexPosn]
                          String
                          (Maybe (String, Type AlexPosn))
                          (PreFunction AlexPosn)
                          (Declaration AlexPosn)
                          (Declaration AlexPosn)
                          (Declaration AlexPosn)
                          [Declaration AlexPosn]
                          String
                          (Maybe (Type AlexPosn))
                          [Arg AlexPosn]
                          [SortArg AlexPosn]
                          (Maybe [SortArg AlexPosn])
                          (Declaration AlexPosn)
                          (Fixity AlexPosn)
                          String
                          [String]
                          (StackFunction AlexPosn)
                          [Declaration AlexPosn]
                          (Declaration AlexPosn)
                          (DataSortLeaf AlexPosn)
                          [DataSortLeaf AlexPosn]
                          (Declaration AlexPosn)
                          (Declaration AlexPosn)
                          (Declaration AlexPosn))
                     -> HappyStk
                          (HappyAbsSyn
                             (ATS AlexPosn)
                             [Declaration AlexPosn]
                             [Type AlexPosn]
                             [Type AlexPosn]
                             (Type AlexPosn)
                             [Arg AlexPosn]
                             [Arg AlexPosn]
                             (Arg AlexPosn)
                             (Arg AlexPosn)
                             (Expression AlexPosn)
                             [Pattern AlexPosn]
                             (Pattern AlexPosn)
                             [(Pattern AlexPosn, LambdaType AlexPosn, Expression AlexPosn)]
                             [(Expression AlexPosn, LambdaType AlexPosn, Expression AlexPosn)]
                             (Maybe [Expression AlexPosn], [Expression AlexPosn])
                             [Expression AlexPosn]
                             [Expression AlexPosn]
                             (LambdaType AlexPosn)
                             (LambdaType AlexPosn)
                             (Expression AlexPosn)
                             [Type AlexPosn]
                             (Expression AlexPosn)
                             [StaticExpression AlexPosn]
                             [Declaration AlexPosn]
                             (StaticExpression AlexPosn)
                             (Expression AlexPosn)
                             (AlexPosn, StaticExpression AlexPosn)
                             (Sort AlexPosn)
                             [String]
                             (Existential AlexPosn)
                             [StaticExpression AlexPosn]
                             (Universal AlexPosn)
                             [[Type AlexPosn]]
                             [[Type AlexPosn]]
                             (Either (StaticExpression AlexPosn) (Expression AlexPosn))
                             (Implementation AlexPosn)
                             (Implementation AlexPosn)
                             (Name AlexPosn)
                             (Name AlexPosn)
                             [(String, Expression AlexPosn)]
                             [(String, Type AlexPosn)]
                             [String]
                             (Maybe (Type AlexPosn))
                             [StaticExpression AlexPosn]
                             (Leaf AlexPosn)
                             [Leaf AlexPosn]
                             [Universal AlexPosn]
                             (Maybe (StaticExpression AlexPosn))
                             (UnOp AlexPosn)
                             (BinOp AlexPosn)
                             (Maybe (String, Type AlexPosn) -> (b0, b0) -> b0)
                             (DataPropLeaf AlexPosn)
                             [DataPropLeaf AlexPosn]
                             String
                             (Maybe (String, Type AlexPosn))
                             (PreFunction AlexPosn)
                             (Declaration AlexPosn)
                             (Declaration AlexPosn)
                             (Declaration AlexPosn)
                             [Declaration AlexPosn]
                             String
                             (Maybe (Type AlexPosn))
                             [Arg AlexPosn]
                             [SortArg AlexPosn]
                             (Maybe [SortArg AlexPosn])
                             (Declaration AlexPosn)
                             (Fixity AlexPosn)
                             String
                             [String]
                             (StackFunction AlexPosn)
                             [Declaration AlexPosn]
                             (Declaration AlexPosn)
                             (DataSortLeaf AlexPosn)
                             [DataSortLeaf AlexPosn]
                             (Declaration AlexPosn)
                             (Declaration AlexPosn)
                             (Declaration AlexPosn))
    • In the third argument of ‘happyReduce’, namely
        ‘happyReduction_340’
      In the expression: happyReduce 6# 55# happyReduction_340
      In an equation for ‘happyReduce_340’:
          happyReduce_340 = happyReduce 6# 55# happyReduction_340
     |
4832 | happyReduce_340 = happyReduce 6# 55# happyReduction_340
     |                                      ^^^^^^^^^^^^^^^^^^

/home/vanessa/programming/haskell/done/ats/dist-newstyle/build/x86_64-linux/ghc-8.2.2/language-ats-1.0.1.0/opt/build/Language/ATS/Parser.hs:4845:38: error:
    • Couldn't match expected type ‘Maybe String’
                  with actual type ‘Bool’
    • In the second argument of ‘PreF’, namely
        ‘(fst < happy_var_6 happy_var_5)’
      In the first argument of ‘happyIn59’, namely
        ‘((PreF
             happy_var_1
             (fst < happy_var_6 happy_var_5)
             []
             []
             happy_var_3
             (snd < happy_var_6 happy_var_5)
             Nothing
             happy_var_6))’
      In the first argument of ‘HappyStk’, namely
        ‘happyIn59
           ((PreF
               happy_var_1
               (fst < happy_var_6 happy_var_5)
               []
               []
               happy_var_3
               (snd < happy_var_6 happy_var_5)
               Nothing
               happy_var_6))’
     |
4845 |                  ((PreF happy_var_1 (fst <happy_var_6 happy_var_5) [] [] happy_var_3 (snd <happy_var_6 happy_var_5) Nothing happy_var_6)
     |                                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^

/home/vanessa/programming/haskell/done/ats/dist-newstyle/build/x86_64-linux/ghc-8.2.2/language-ats-1.0.1.0/opt/build/Language/ATS/Parser.hs:4845:87: error:
    • Couldn't match expected type ‘Maybe (Type a)’
                  with actual type ‘Bool’
    • In the sixth argument of ‘PreF’, namely
        ‘(snd < happy_var_6 happy_var_5)’
      In the first argument of ‘happyIn59’, namely
        ‘((PreF
             happy_var_1
             (fst < happy_var_6 happy_var_5)
             []
             []
             happy_var_3
             (snd < happy_var_6 happy_var_5)
             Nothing
             happy_var_6))’
      In the first argument of ‘HappyStk’, namely
        ‘happyIn59
           ((PreF
               happy_var_1
               (fst < happy_var_6 happy_var_5)
               []
               []
               happy_var_3
               (snd < happy_var_6 happy_var_5)
               Nothing
               happy_var_6))’
    • Relevant bindings include
        happy_var_3 :: [Arg a]
          (bound at /home/vanessa/programming/haskell/done/ats/dist-newstyle/build/x86_64-linux/ghc-8.2.2/language-ats-1.0.1.0/opt/build/Language/ATS/Parser.hs:4841:39)
        happy_var_1 :: Name a
          (bound at /home/vanessa/programming/haskell/done/ats/dist-newstyle/build/x86_64-linux/ghc-8.2.2/language-ats-1.0.1.0/opt/build/Language/ATS/Parser.hs:4840:43)
        happyRest :: HappyStk
                       (HappyAbsSyn
                          t4
                          t5
                          t6
                          t7
                          t8
                          [Arg a]
                          t10
                          t11
                          t12
                          t13
                          t14
                          t15
                          t16
                          t17
                          t18
                          t19
                          t20
                          t21
                          t22
                          t23
                          t24
                          t25
                          t26
                          t27
                          t28
                          t29
                          t30
                          t31
                          t32
                          t33
                          t34
                          t35
                          t36
                          t37
                          t38
                          t39
                          t40
                          (Name a)
                          t42
                          t43
                          t44
                          t45
                          t46
                          t47
                          t48
                          t49
                          t50
                          t51
                          t52
                          t53
                          (t58 -> (b, b) -> b)
                          t55
                          t56
                          t57
                          t58
                          (PreFunction a)
                          t60
                          t61
                          t62
                          t63
                          t64
                          t65
                          t66
                          t67
                          t68
                          t69
                          t70
                          t71
                          t72
                          t73
                          t74
                          t75
                          t76
                          t77
                          t78
                          t79
                          t80)
          (bound at /home/vanessa/programming/haskell/done/ats/dist-newstyle/build/x86_64-linux/ghc-8.2.2/language-ats-1.0.1.0/opt/build/Language/ATS/Parser.hs:4839:9)
        happy_x_1 :: HappyAbsSyn
                       t4
                       t5
                       t6
                       t7
                       t8
                       [Arg a]
                       t10
                       t11
                       t12
                       t13
                       t14
                       t15
                       t16
                       t17
                       t18
                       t19
                       t20
                       t21
                       t22
                       t23
                       t24
                       t25
                       t26
                       t27
                       t28
                       t29
                       t30
                       t31
                       t32
                       t33
                       t34
                       t35
                       t36
                       t37
                       t38
                       t39
                       t40
                       (Name a)
                       t42
                       t43
                       t44
                       t45
                       t46
                       t47
                       t48
                       t49
                       t50
                       t51
                       t52
                       t53
                       (t58 -> (b, b) -> b)
                       t55
                       t56
                       t57
                       t58
                       (PreFunction a)
                       t60
                       t61
                       t62
                       t63
                       t64
                       t65
                       t66
                       t67
                       t68
                       t69
                       t70
                       t71
                       t72
                       t73
                       t74
                       t75
                       t76
                       t77
                       t78
                       t79
                       t80
          (bound at /home/vanessa/programming/haskell/done/ats/dist-newstyle/build/x86_64-linux/ghc-8.2.2/language-ats-1.0.1.0/opt/build/Language/ATS/Parser.hs:4838:9)
        happy_x_2 :: HappyAbsSyn
                       t4
                       t5
                       t6
                       t7
                       t8
                       [Arg a]
                       t10
                       t11
                       t12
                       t13
                       t14
                       t15
                       t16
                       t17
                       t18
                       t19
                       t20
                       t21
                       t22
                       t23
                       t24
                       t25
                       t26
                       t27
                       t28
                       t29
                       t30
                       t31
                       t32
                       t33
                       t34
                       t35
                       t36
                       t37
                       t38
                       t39
                       t40
                       (Name a)
                       t42
                       t43
                       t44
                       t45
                       t46
                       t47
                       t48
                       t49
                       t50
                       t51
                       t52
                       t53
                       (t58 -> (b, b) -> b)
                       t55
                       t56
                       t57
                       t58
                       (PreFunction a)
                       t60
                       t61
                       t62
                       t63
                       t64
                       t65
                       t66
                       t67
                       t68
                       t69
                       t70
                       t71
                       t72
                       t73
                       t74
                       t75
                       t76
                       t77
                       t78
                       t79
                       t80
          (bound at /home/vanessa/programming/haskell/done/ats/dist-newstyle/build/x86_64-linux/ghc-8.2.2/language-ats-1.0.1.0/opt/build/Language/ATS/Parser.hs:4837:9)
        happy_x_3 :: HappyAbsSyn
                       t4
                       t5
                       t6
                       t7
                       t8
                       [Arg a]
                       t10
                       t11
                       t12
                       t13
                       t14
                       t15
                       t16
                       t17
                       t18
                       t19
                       t20
                       t21
                       t22
                       t23
                       t24
                       t25
                       t26
                       t27
                       t28
                       t29
                       t30
                       t31
                       t32
                       t33
                       t34
                       t35
                       t36
                       t37
                       t38
                       t39
                       t40
                       (Name a)
                       t42
                       t43
                       t44
                       t45
                       t46
                       t47
                       t48
                       t49
                       t50
                       t51
                       t52
                       t53
                       (t58 -> (b, b) -> b)
                       t55
                       t56
                       t57
                       t58
                       (PreFunction a)
                       t60
                       t61
                       t62
                       t63
                       t64
                       t65
                       t66
                       t67
                       t68
                       t69
                       t70
                       t71
                       t72
                       t73
                       t74
                       t75
                       t76
                       t77
                       t78
                       t79
                       t80
          (bound at /home/vanessa/programming/haskell/done/ats/dist-newstyle/build/x86_64-linux/ghc-8.2.2/language-ats-1.0.1.0/opt/build/Language/ATS/Parser.hs:4836:9)
        (Some bindings suppressed; use -fmax-relevant-binds=N or -fno-max-relevant-binds)
     |
4845 |                  ((PreF happy_var_1 (fst <happy_var_6 happy_var_5) [] [] happy_var_3 (snd <happy_var_6 happy_var_5) Nothing happy_var_6)
     |                                                                                       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^

/home/vanessa/programming/haskell/done/ats/dist-newstyle/build/x86_64-linux/ghc-8.2.2/language-ats-1.0.1.0/opt/build/Language/ATS/Parser.hs:4845:125: error:
    • Couldn't match expected type ‘Maybe (Expression a)’
                  with actual type ‘t58 -> (b, b) -> b’
    • Probable cause: ‘happy_var_6’ is applied to too few arguments
      In the 8th argument of ‘PreF’, namely ‘happy_var_6’
      In the first argument of ‘happyIn59’, namely
        ‘((PreF
             happy_var_1
             (fst < happy_var_6 happy_var_5)
             []
             []
             happy_var_3
             (snd < happy_var_6 happy_var_5)
             Nothing
             happy_var_6))’
      In the first argument of ‘HappyStk’, namely
        ‘happyIn59
           ((PreF
               happy_var_1
               (fst < happy_var_6 happy_var_5)
               []
               []
               happy_var_3
               (snd < happy_var_6 happy_var_5)
               Nothing
               happy_var_6))’
    • Relevant bindings include
        happy_var_6 :: t58 -> (b, b) -> b
          (bound at /home/vanessa/programming/haskell/done/ats/dist-newstyle/build/x86_64-linux/ghc-8.2.2/language-ats-1.0.1.0/opt/build/Language/ATS/Parser.hs:4843:40)
        happy_var_5 :: t58
          (bound at /home/vanessa/programming/haskell/done/ats/dist-newstyle/build/x86_64-linux/ghc-8.2.2/language-ats-1.0.1.0/opt/build/Language/ATS/Parser.hs:4842:40)
        happy_var_3 :: [Arg a]
          (bound at /home/vanessa/programming/haskell/done/ats/dist-newstyle/build/x86_64-linux/ghc-8.2.2/language-ats-1.0.1.0/opt/build/Language/ATS/Parser.hs:4841:39)
        happy_var_1 :: Name a
          (bound at /home/vanessa/programming/haskell/done/ats/dist-newstyle/build/x86_64-linux/ghc-8.2.2/language-ats-1.0.1.0/opt/build/Language/ATS/Parser.hs:4840:43)
        happyRest :: HappyStk
                       (HappyAbsSyn
                          t4
                          t5
                          t6
                          t7
                          t8
                          [Arg a]
                          t10
                          t11
                          t12
                          t13
                          t14
                          t15
                          t16
                          t17
                          t18
                          t19
                          t20
                          t21
                          t22
                          t23
                          t24
                          t25
                          t26
                          t27
                          t28
                          t29
                          t30
                          t31
                          t32
                          t33
                          t34
                          t35
                          t36
                          t37
                          t38
                          t39
                          t40
                          (Name a)
                          t42
                          t43
                          t44
                          t45
                          t46
                          t47
                          t48
                          t49
                          t50
                          t51
                          t52
                          t53
                          (t58 -> (b, b) -> b)
                          t55
                          t56
                          t57
                          t58
                          (PreFunction a)
                          t60
                          t61
                          t62
                          t63
                          t64
                          t65
                          t66
                          t67
                          t68
                          t69
                          t70
                          t71
                          t72
                          t73
                          t74
                          t75
                          t76
                          t77
                          t78
                          t79
                          t80)
          (bound at /home/vanessa/programming/haskell/done/ats/dist-newstyle/build/x86_64-linux/ghc-8.2.2/language-ats-1.0.1.0/opt/build/Language/ATS/Parser.hs:4839:9)
        happy_x_1 :: HappyAbsSyn
                       t4
                       t5
                       t6
                       t7
                       t8
                       [Arg a]
                       t10
                       t11
                       t12
                       t13
                       t14
                       t15
                       t16
                       t17
                       t18
                       t19
                       t20
                       t21
                       t22
                       t23
                       t24
                       t25
                       t26
                       t27
                       t28
                       t29
                       t30
                       t31
                       t32
                       t33
                       t34
                       t35
                       t36
                       t37
                       t38
                       t39
                       t40
                       (Name a)
                       t42
                       t43
                       t44
                       t45
                       t46
                       t47
                       t48
                       t49
                       t50
                       t51
                       t52
                       t53
                       (t58 -> (b, b) -> b)
                       t55
                       t56
                       t57
                       t58
                       (PreFunction a)
                       t60
                       t61
                       t62
                       t63
                       t64
                       t65
                       t66
                       t67
                       t68
                       t69
                       t70
                       t71
                       t72
                       t73
                       t74
                       t75
                       t76
                       t77
                       t78
                       t79
                       t80
          (bound at /home/vanessa/programming/haskell/done/ats/dist-newstyle/build/x86_64-linux/ghc-8.2.2/language-ats-1.0.1.0/opt/build/Language/ATS/Parser.hs:4838:9)
        (Some bindings suppressed; use -fmax-relevant-binds=N or -fno-max-relevant-binds)
     |
4845 |                  ((PreF happy_var_1 (fst <happy_var_6 happy_var_5) [] [] happy_var_3 (snd <happy_var_6 happy_var_5) Nothing happy_var_6)
     |                                                                                                                             ^^^^^^^^^^^

I didn't see anything in the manual indicating that this would not be allowed. I think it would be nice to have happy return some sort of error message before GHC does - the one I ran into was not particularly user-friendly.

Thanks!

anka-213 commented 3 years ago

Why was this closed? This is still an issue.

Ericson2314 commented 3 years ago

Reopening if it is still an issue.

int-index commented 3 years ago

The name of the issue is misleading

happy fails to generate valid Haskell when <$> is used.

It generates valid Haskell, just not the Haskell that you expect. Happy treats <$> as < followed by $>, where $> is a reference much like $1, $2, $3, etc, that refers to the last (rightmost) item.

Something like fn <$> arg turns into fn <happy_var_n arg, which is of course valid Haskell – it is the use of the < operator.

One way to fix this would be to abstain from substituting $-references if they are preceded by a symbol that could be a Haskell operator.

sgraf812 commented 2 months ago

I suggest we simply emit an error when <$> is used in code fragments. When the user meant <$>, they could use fmap instead. When the user meant < $> (as in 1 < $>), then the user can just insert a space.