ghc/compiler/tests/typecheck/should_succeed/tc065.stderr

   1
   2
   3 --================================================================================
   4 Typechecked:
   5 {- nonrec -}
   6 {- nonrec -}
   7 Succeeded{-r4G,x-}{i} =
   8     _/\_ a{-r8v-} b{-r8w-} -> \ tpl_B1 ->
   9         Succeeded{-r4G,x-}{i}
  10             {_@_ a{-r8v-} _@_ b{-r8w-} tpl_B1}
  11 Failed{-r4F,x-}{i} =
  12     _/\_ a{-r8v-} b{-r8w-} -> \ tpl_B1 ->
  13         Failed{-r4F,x-}{i}
  14             {_@_ a{-r8v-} _@_ b{-r8w-} tpl_B1}
  15 {- nonrec -}
  16 MkDigraph{-r8L,x-}{i} =
  17     _/\_ vertex{-r8G-} -> \ tpl_B1 ->
  18         MkDigraph{-r8L,x-}{i}
  19             {_@_ vertex{-r8G-} tpl_B1}
  20 {- nonrec -}
  21 {- rec -}
  22 AbsBinds
  23 [a{-a1lz-}, b{-a1lA-}]
  24 []
  25 [([a{-a1lz-}, b{-a1lA-}], $d1{-r1lE,x-}, d.Eval_a1kX)]
  26     d.Eval_a1kX =
  27         ({-dict-} [] [])
  28 {- rec -}
  29 AbsBinds
  30 [vertex{-a1lB-}]
  31 []
  32 [([vertex{-a1lB-}], $d2{-r1lS,x-}, d.Eval_a1l3)]
  33     d.Eval_a1l3 =
  34         ({-dict-} [] [])
  35 {- nonrec -}
  36 d.Monad_a1l5 =
  37     PrelBase.$d24{-rj0,p-}
  38 >>=_a1lQ =
  39     PrelBase.>>={-811,p-}
  40         PrelBase.[]{-3j,p-}
  41         d.Monad_a1l5
  42 d.Monad_a1l8 =
  43     d.Monad_a1l5
  44 return_a1lP =
  45     PrelBase.return{-816,p-}
  46         PrelBase.[]{-3j,p-}
  47         d.Monad_a1l8
  48 d.MonadZero_a1la =
  49     PrelBase.$d23{-riZ,p-}
  50 zero_a1lO =
  51     PrelBase.zero{-810,p-}
  52         PrelBase.[]{-3j,p-}
  53         d.MonadZero_a1la
  54 d.Functor_a1ld =
  55     PrelBase.$d25{-rj1,p-}
  56 map_a1lN =
  57     PrelBase.map{-rkx,p-}
  58         PrelBase.[]{-3j,p-}
  59         d.Functor_a1ld
  60 d.MonadPlus_a1lg =
  61     PrelBase.$d22{-riY,p-}
  62 ++_a1lM =
  63     PrelBase.++{-rnk,p-}
  64         PrelBase.[]{-3j,p-}
  65         d.MonadPlus_a1lg
  66 >>=_a1lL =
  67     >>=_a1lQ
  68 return_a1lK =
  69     return_a1lP
  70 >>=_a1lJ =
  71     >>=_a1lQ
  72 return_a1lI =
  73     return_a1lP
  74 >>=_a1lH =
  75     >>=_a1lQ
  76 return_a1lG =
  77     return_a1lP
  78 zero_a1lF =
  79     zero_a1lO
  80 {- nonrec -}
  81 AbsBinds
  82 [vertex{-a1ba-}]
  83 [d.Eq_a1bl]
  84 [([vertex{-a1ba-}],
  85   isRecursiveCycle{-r6x,x-},
  86   isRecursiveCycle_a1b5)]
  87     d.Eq_a1bp =
  88         d.Eq_a1bl
  89     d.Eq_a1bq =
  90         d.Eq_a1bl
  91     d.Eq_a1bn =
  92         PrelTup.$d9{-rEY,p-}
  93             [vertex{-a1ba-}, vertex{-a1ba-}]
  94             [d.Eq_a1bp, d.Eq_a1bq]
  95     elem_a1lT =
  96         PrelList.elem{-rF6,p-}
  97             (vertex{-a1ba-}, vertex{-a1ba-})
  98             d.Eq_a1bn
  99     isRecursiveCycle_a1b5
 100         [vertex_r8n] edges_r8p
 101                 =   (vertex_r8n, vertex_r8n) elem_a1lT edges_r8p
 102     isRecursiveCycle_a1b5
 103         cycle_r8r edges_r8t
 104                 =   PrelBase.True{-5E,p-}{i}
 105 {- nonrec -}
 106 {- nonrec -}
 107 AbsBinds
 108 [vertex{-a1bC-}, name{-a1bD-}, code{-a1bE-}]
 109 [d.Eq_a1cs, d.Ord_a1ct]
 110 [([name{-a1bD-}, vertex{-a1bC-}, code{-a1bE-}],
 111   lookupVertex{-r6w,x-},
 112   lookupVertex_a1bz)]
 113     d.Eq_a1cv =
 114         d.Eq_a1cs
 115     ==_a1lU =
 116         PrelBase.=={-8Y,p-}
 117             vertex{-a1bC-}
 118             d.Eq_a1cv
 119     lookupVertex_a1bz
 120         flat_info_r8e vertex_r8g
 121                 =   PrelList.head{-rFm,p-}
 122                         code{-a1bE-} code_list_r8i
 123                 where
 124                     {- nonrec -}
 125                     AbsBinds [] [] [([], code_list_r8i, code_list_a1bI)]
 126                         code_list_a1bI
 127                             =   [ code_r8l |
 128                                     (vertex'_r8k, _, _, code_r8l) <- flat_info_r8e, vertex_r8g
 129                                                                                     ==_a1lU vertex'_r8k
 130                                     ]
 131                     {- nonrec -}
 132 {- nonrec -}
 133 {- nonrec -}
 134 AbsBinds
 135 [vertex{-a1cO-}, name{-a1cR-}, code{-a1cS-}]
 136 [d.Eq_a1ei, d.Ord_a1ej]
 137 [([name{-a1cR-}, code{-a1cS-}, vertex{-a1cO-}],
 138   mkEdges{-r6v,x-},
 139   mkEdges_a1cL)]
 140     d.Ord_a1ek =
 141         d.Ord_a1ej
 142     d.MonadZero_a1el =
 143         PrelBase.$d23{-riZ,p-}
 144     mkEdges_a1cL
 145         vertices_r7U flat_info_r7W
 146                 =   [ (source_vertex_r87, target_vertex_r8c) |
 147                         (source_vertex_r87, _, used_names_r88, _) <- flat_info_r7W, target_name_r8a <- Set.setToList{-rhd,p-}
 148                                                                                                            name{-a1cR-} used_names_r88, target_vertex_r8c <- vertices_defining_a1lV target_name_r8a
 149                                                                                                                                                                                     flat_info_r7W
 150                         ]
 151                 where
 152                     {- nonrec -}
 153                     AbsBinds
 154                     [t{-a1d5-}, t{-a1da-}, t{-a1dd-}, a{-a1dg-}, a{-a1di-}]
 155                     [d.Ord_a1du, d.MonadZero_a1dA]
 156                     [([t{-a1d5-}, t{-a1da-}, t{-a1dd-}, a{-a1dg-}, a{-a1di-}],
 157                       vertices_defining_r7Y,
 158                       vertices_defining_a1cU)]
 159                         d.Monad_a1dw =
 160                             PrelBase.scsel_MonadZeroPrelBaseMonad{-a1m0,p-}
 161                                 a{-a1dg-}
 162                                 d.MonadZero_a1dA
 163                         elementOf_a1lZ =
 164                             Set.elementOf{-rh5,p-}
 165                                 a{-a1di-}
 166                                 d.Ord_a1du
 167                         >>=_a1lY =
 168                             PrelBase.>>={-811,p-}
 169                                 a{-a1dg-}
 170                                 d.Monad_a1dw
 171                         d.Monad_a1dy =
 172                             d.Monad_a1dw
 173                         return_a1lX =
 174                             PrelBase.return{-816,p-}
 175                                 a{-a1dg-}
 176                                 d.Monad_a1dy
 177                         zero_a1lW =
 178                             PrelBase.zero{-810,p-}
 179                                 a{-a1dg-}
 180                                 d.MonadZero_a1dA
 181                         vertices_defining_a1cU
 182                             name_r80 flat_info_r82
 183                                     =   [ vertex_r84 |
 184                                             (vertex_r84, names_defined_r85, _, _) <- flat_info_r82, name_r80
 185                                                                                                     elementOf_a1lZ names_defined_r85
 186                                             ]
 187                     {- nonrec -}
 188                     vertices_defining_a1lV =
 189                         vertices_defining_r7Y
 190                             [vertex{-a1cO-}, Set.Set{-rh2,p-} name{-a1cR-}, code{-a1cS-}, PrelBase.[]{-3j,p-}, name{-a1cR-}]
 191                             [d.Ord_a1ek, d.MonadZero_a1el]
 192 {- nonrec -}
 193 {- nonrec -}
 194 AbsBinds
 195 [vertex{-a1eC-}, name{-a1eD-}, code{-a1eE-}]
 196 []
 197 [([name{-a1eD-}, code{-a1eE-}, vertex{-a1eC-}],
 198   mkVertices{-r6u,x-},
 199   mkVertices_a1ez)]
 200     mkVertices_a1ez
 201         info_r7Q
 202                 =   [ vertex_r7S |
 203                         (vertex_r7S, _, _, _) <- info_r7Q ]
 204 {- nonrec -}
 205 {- nonrec -}
 206 AbsBinds
 207 [vertex{-a1ff-}]
 208 [d.Eq_a1fs]
 209 [([vertex{-a1ff-}], isCyclic{-r6s,x-}, isCyclic_a1fc)]
 210     d.Eq_a1fw =
 211         d.Eq_a1fs
 212     d.Eq_a1fx =
 213         d.Eq_a1fs
 214     d.Eq_a1fu =
 215         PrelTup.$d9{-rEY,p-}
 216             [vertex{-a1ff-}, vertex{-a1ff-}]
 217             [d.Eq_a1fw, d.Eq_a1fx]
 218     elem_a1m1 =
 219         PrelList.elem{-rF6,p-}
 220             (vertex{-a1ff-}, vertex{-a1ff-})
 221             d.Eq_a1fu
 222     isCyclic_a1fc
 223         edges_r7w [v_r7y]
 224                 =   (v_r7y, v_r7y) elem_a1m1 edges_r7w
 225     isCyclic_a1fc
 226         edges_r7A vs_r7C
 227                 =   PrelBase.True{-5E,p-}{i}
 228 {- nonrec -}
 229 {- rec -}
 230 AbsBinds
 231 [t{-a1gi-}]
 232 [d.Eq_a1gA]
 233 [([t{-a1gi-}], dfs{-r6y,x-}, dfs_a1fz)]
 234     elem_a1m2 =
 235         PrelList.elem{-rF6,p-}
 236             t{-a1gi-}
 237             d.Eq_a1gA
 238     dfs_a1fz
 239         r_r7f (vs_r7h, ns_r7i) PrelBase.[]{-5i,p-}{i}
 240                 =   (vs_r7h, ns_r7i)
 241     dfs_a1fz
 242         r_r7l (vs_r7n, ns_r7o) (x_r7q PrelBase.:{-55,p-}{i} xs_r7r)
 243                 | [x_r7q elem_a1m2 vs_r7n] =
 244                     dfs_a1fz r_r7l (vs_r7n, ns_r7o) xs_r7r
 245                 | [PrelBase.otherwise{-818,p-}] =
 246                     dfs_a1fz r_r7l
 247                              (vs'_r7t,
 248                               ++_a1lM
 249                                   t{-a1gi-}
 250                                   (PrelBase.:{-55,p-}{i}
 251                                        t{-a1gi-}
 252                                        x_r7q ns'_r7u)
 253                                   ns_r7o)
 254                              xs_r7r
 255                 where
 256                     {- nonrec -}
 257                     AbsBinds [] [] [([], vs'_r7t, vs'_a1g4), ([], ns'_r7u, ns'_a1g5)]
 258                         (vs'_a1g4, ns'_a1g5)
 259                             =   dfs_a1fz r_r7l
 260                                          (PrelBase.:{-55,p-}{i}
 261                                               t{-a1gi-}
 262                                               x_r7q vs_r7n,
 263                                           PrelBase.[]{-5i,p-}{i}
 264                                               t{-a1gi-})
 265                                          r_r7l x_r7q
 266                     {- nonrec -}
 267 {- nonrec -}
 268 {- nonrec -}
 269 AbsBinds
 270 [vertex{-a1gK-}]
 271 [d.Eq_a1ju]
 272 [([vertex{-a1gK-}],
 273   stronglyConnComp{-r6r,x-},
 274   stronglyConnComp_a1gH)]
 275     d.Eq_a1jv =
 276         d.Eq_a1ju
 277     d.Eq_a1jq =
 278         d.Eq_a1ju
 279     d.Eq_a1jx =
 280         d.Eq_a1ju
 281     dfs_a1m3 =
 282         dfs{-r6y,x-}
 283             vertex{-a1gK-}
 284             d.Eq_a1jx
 285     d.Eq_a1jr =
 286         d.Eq_a1ju
 287     stronglyConnComp_a1gH
 288         es_r6B vs_r6D
 289                 =   PrelTup.snd{-rF4,p-}
 290                         [[vertex{-a1gK-}], [[vertex{-a1gK-}]]] span_tree_a1m4 new_range_a1m6 reversed_edges_r6F
 291                                                                               (PrelBase.[]{-5i,p-}{i}
 292                                                                                    vertex{-a1gK-},
 293                                                                                PrelBase.[]{-5i,p-}{i}
 294                                                                                    [vertex{-a1gK-}])
 295                                                                               PrelTup.snd{-rF4,p-}
 296                                                                                   [[vertex{-a1gK-}], [vertex{-a1gK-}]] dfs_a1m3 new_range_a1m5 es_r6B
 297                                                                                                                                 (PrelBase.[]{-5i,p-}{i}
 298                                                                                                                                      vertex{-a1gK-},
 299                                                                                                                                  PrelBase.[]{-5i,p-}{i}
 300                                                                                                                                      vertex{-a1gK-})
 301                                                                                                                                 vs_r6D
 302                 where
 303                     {- rec -}
 304                     AbsBinds
 305                     [t{-a1h2-}]
 306                     [d.Eq_a1hJ]
 307                     [([t{-a1h2-}], span_tree_r6I, span_tree_a1gO)]
 308                         elem_a1m8 =
 309                             PrelList.elem{-rF6,p-}
 310                                 t{-a1h2-}
 311                                 d.Eq_a1hJ
 312                         d.Eq_a1hL =
 313                             d.Eq_a1hJ
 314                         dfs_a1m7 =
 315                             dfs{-r6y,x-}
 316                                 t{-a1h2-}
 317                                 d.Eq_a1hL
 318                         span_tree_a1gO
 319                             r_r6Y (vs_r70, ns_r71) PrelBase.[]{-5i,p-}{i}
 320                                     =   (vs_r70, ns_r71)
 321                         span_tree_a1gO
 322                             r_r74 (vs_r76, ns_r77) (x_r79 PrelBase.:{-55,p-}{i} xs_r7a)
 323                                     | [x_r79 elem_a1m8 vs_r76] =
 324                                         span_tree_a1gO r_r74 (vs_r76, ns_r77) xs_r7a
 325                                     | [PrelBase.otherwise{-818,p-}] =
 326                                         span_tree_a1gO r_r74
 327                                                        (vs'_r7c,
 328                                                         PrelBase.:{-55,p-}{i}
 329                                                             [t{-a1h2-}]
 330                                                             (PrelBase.:{-55,p-}{i}
 331                                                                  t{-a1h2-}
 332                                                                  x_r79 ns'_r7d)
 333                                                             ns_r77)
 334                                                        xs_r7a
 335                                     where
 336                                         {- nonrec -}
 337                                         AbsBinds
 338                                         []
 339                                         []
 340                                         [([], vs'_r7c, vs'_a1hj), ([], ns'_r7d, ns'_a1hk)]
 341                                             (vs'_a1hj, ns'_a1hk)
 342                                                 =   dfs_a1m7 r_r74
 343                                                              (PrelBase.:{-55,p-}{i}
 344                                                                   t{-a1h2-}
 345                                                                   x_r79 vs_r76,
 346                                                               PrelBase.[]{-5i,p-}{i}
 347                                                                   t{-a1h2-})
 348                                                              r_r74 x_r79
 349                                         {- nonrec -}
 350                     {- nonrec -}
 351                     span_tree_a1m4 =
 352                         span_tree_r6I
 353                             vertex{-a1gK-}
 354                             d.Eq_a1jv
 355                     {- rec -}
 356                     AbsBinds
 357                     [t{-a1hV-}, t{-a1i0-}]
 358                     [d.Eq_a1ig]
 359                     [([t{-a1hV-}, t{-a1i0-}], new_range_r6H, new_range_a1hN)]
 360                         ==_a1m9 =
 361                             PrelBase.=={-8Y,p-}
 362                                 t{-a1i0-}
 363                                 d.Eq_a1ig
 364                         new_range_a1hN
 365                             PrelBase.[]{-5i,p-}{i} w_r6Q
 366                                     =   PrelBase.[]{-5i,p-}{i}
 367                                             t{-a1hV-}
 368                         new_range_a1hN
 369                             ((x_r6S, y_r6T) PrelBase.:{-55,p-}{i} xys_r6U) w_r6W
 370                                     =   if x_r6S ==_a1m9 w_r6W then
 371                                             PrelBase.:{-55,p-}{i}
 372                                                 t{-a1hV-}
 373                                                 y_r6T (new_range_a1hN xys_r6U w_r6W)
 374                                         else
 375                                             new_range_a1hN xys_r6U w_r6W
 376                     {- nonrec -}
 377                     new_range_a1m6 =
 378                         new_range_r6H
 379                             [vertex{-a1gK-}, vertex{-a1gK-}]
 380                             d.Eq_a1jq
 381                     new_range_a1m5 =
 382                         new_range_r6H
 383                             [vertex{-a1gK-}, vertex{-a1gK-}]
 384                             d.Eq_a1jr
 385                     {- nonrec -}
 386                     AbsBinds [v{-a1iv-}] [] [([v{-a1iv-}], swap_r6G, swap_a1im)]
 387                         swap_a1im
 388                             (x_r6M, y_r6N)
 389                                     =   (y_r6N, x_r6M)
 390                     {- nonrec -}
 391                     {- nonrec -}
 392                     AbsBinds [] [] [([], reversed_edges_r6F, reversed_edges_a1iy)]
 393                         reversed_edges_a1iy
 394                             =   map_a1lN
 395                                     [Edge{-r8K,x-} vertex{-a1gK-}, Edge{-r8K,x-} vertex{-a1gK-}] swap_r6G
 396                                                                                                      vertex{-a1gK-}
 397                                                                                                  es_r6B
 398                     {- nonrec -}
 399 {- nonrec -}
 400 {- nonrec -}
 401 AbsBinds
 402 [vertex{-a1jI-}]
 403 [d.Eq_a1kA]
 404 [([vertex{-a1jI-}], topSort{-r6t,x-}, topSort_a1jF)]
 405     d.Eq_a1kI =
 406         d.Eq_a1kA
 407     isCyclic_a1mb =
 408         isCyclic{-r6s,x-}
 409             vertex{-a1jI-}
 410             d.Eq_a1kI
 411     d.Eq_a1kK =
 412         d.Eq_a1kA
 413     stronglyConnComp_a1ma =
 414         stronglyConnComp{-r6r,x-}
 415             vertex{-a1jI-}
 416             d.Eq_a1kK
 417     topSort_a1jF
 418         edges_r7E vertices_r7G
 419                 =   case cycles_r7J of
 420                       PrelBase.[]{-5i,p-}{i}
 421                               ->  Succeeded{-r4G,x-}{i}
 422                                       [[vertex{-a1jI-}], [[vertex{-a1jI-}]]] [ v_r7N |
 423                                                                                  [v_r7N] <- singletons_r7K
 424                                                                                  ]
 425                       _       ->  Failed{-r4F,x-}{i}
 426                                       [[vertex{-a1jI-}], [[vertex{-a1jI-}]]] cycles_r7J
 427                 where
 428                     {- nonrec -}
 429                     AbsBinds [] [] [([], sccs_r7I, sccs_a1jM)]
 430                         sccs_a1jM
 431                             =   stronglyConnComp_a1ma edges_r7E vertices_r7G
 432                     {- nonrec -}
 433                     {- nonrec -}
 434                     AbsBinds
 435                     []
 436                     []
 437                     [([], cycles_r7J, cycles_a1jT), ([],
 438                                                      singletons_r7K,
 439                                                      singletons_a1jU)]
 440                         (cycles_a1jT, singletons_a1jU)
 441                             =   List.partition{-rhM,p-}
 442                                     [vertex{-a1jI-}] isCyclic_a1mb edges_r7E sccs_r7I
 443                     {- nonrec -}
 444 {- nonrec -}
 445 {- nonrec -}
 446 AbsBinds
 447 [vertex{-a1kQ-}]
 448 []
 449 [([vertex{-a1kQ-}], mkDigraph{-r6z,x-}, mkDigraph_a1kM)]
 450     mkDigraph_a1kM
 451         =   MkDigraph{-r8L,x-}{i}
 452                 vertex{-a1kQ-}
 453 {- nonrec -}
 454 ghc: module version changed to 1; reason: no old .hi file
 455 _interface_ Digraphs 1
 456 _instance_modules_
 457 ArrBase Foreign IO PrelNum
 458 _usages_
 459 List 1 :: partition 1;
 460 PrelBase 1 :: $d14 1 $d15 1 $d22 1 $d23 1 $d24 1 $d25 1 $d26 1 $d27 1 $d32 1 $d34 1 $d37 1 $d39 1 $d41 1 $d44 1 $d45 1 $d46 1 $d49 1 $d51 1 $d6 1 $d7 1 otherwise 1 Eq 1 Eval 1 Functor 1 Monad 1 MonadPlus 1 MonadZero 1 Ord 1 Ordering 1;
 461 PrelList 1 :: elem 1 head 1;
 462 PrelNum 1 :: $d17 1 $d18 1;
 463 PrelTup 1 :: $d11 1 $d13 1 $d15 1 $d49 1 $d51 1 $d9 1 snd 1;
 464 Set 2 :: $d1 2 elementOf 2 setToList 2 Set 1;
 465 _exports_
 466 Digraphs dfs isCyclic isRecursiveCycle lookupVertex mkDigraph mkEdges mkVertices stronglyConnComp topSort Cycle Digraph(MkDigraph) Edge FlattenedDependencyInfo MaybeErr(Succeeded Failed);
 467 _instances_
 468 instance _forall_ [a b] => {PrelBase.Eval (MaybeErr a b)} = $d1;
 469 instance _forall_ [a] => {PrelBase.Eval (Digraph a)} = $d2;
 470 _declarations_
 471 1 $d1 _:_ _forall_ [a b] => {PrelBase.Eval (MaybeErr a b)} ;;
 472 1 $d2 _:_ _forall_ [a] => {PrelBase.Eval (Digraph a)} ;;
 473 1 type Cycle r8C = [r8C] ;
 474 1 data Digraph r8G = MkDigraph [r8G] ;
 475 1 type Edge r8E = (r8E, r8E) ;
 476 1 type FlattenedDependencyInfo r8y r8z r8A = [(r8y, Set.Set r8z, Set.Set r8z, r8A)] ;
 477 1 data MaybeErr r8v r8w = Succeeded r8v |  Failed r8w ;
 478 1 dfs _:_ _forall_ [a] {PrelBase.Eq a} => (a -> [a]) -> ([a], [a]) -> [a] -> ([a], [a]) ;;
 479 1 isCyclic _:_ _forall_ [a] {PrelBase.Eq a} => [Edge a] -> [a] -> PrelBase.Bool ;;
 480 1 isRecursiveCycle _:_ _forall_ [a] {PrelBase.Eq a} => Cycle a -> [Edge a] -> PrelBase.Bool ;;
 481 1 lookupVertex _:_ _forall_ [a b c] {PrelBase.Eq b, PrelBase.Ord a} => FlattenedDependencyInfo b a c -> b -> c ;;
 482 1 mkDigraph _:_ _forall_ [a] => [a] -> Digraph a ;;
 483 1 mkEdges _:_ _forall_ [a b c] {PrelBase.Eq c, PrelBase.Ord a} => [c] -> FlattenedDependencyInfo c a b -> [Edge c] ;;
 484 1 mkVertices _:_ _forall_ [a b c] => FlattenedDependencyInfo c a b -> [c] ;;
 485 1 stronglyConnComp _:_ _forall_ [a] {PrelBase.Eq a} => [Edge a] -> [a] -> [[a]] ;;
 486 1 topSort _:_ _forall_ [a] {PrelBase.Eq a} => [Edge a] -> [a] -> MaybeErr [a] [[a]] ;;