Class methods that are not in scope can cause internal errors

Consider the following modules:

module M where

class C a where
  methodC :: a

module N (C) where

import M

module O where

import N

f :: C a => a
f = methodC

In O, methodC should not be in scope and when compiling the module with PAKCS, an appropriate error message should be reported. Instead, we get the following internal error, which basically states that funType in the dictionary transformation module has not found M.methodC in the value environment:

Prelude> :l O
[1 of 4] Skipping  Prelude          ( /home/leif/pakcs-3.2.0/lib/Prelude.curry, /home/leif/pakcs-3.2.0/lib/.curry/pakcs-3.2.0/Prelude.fcy )
[2 of 4] Compiling M                ( M.curry, .curry/pakcs-3.2.0/M.fcy )
[3 of 4] Compiling N                ( N.curry, .curry/pakcs-3.2.0/N.fcy )
[4 of 4] Compiling O                ( O.curry, .curry/pakcs-3.2.0/O.fcy )
pakcs-frontend: Internal error: Dictionary.funType QualIdent {qidSpanInfo = SpanInfo {srcSpan = Span {file = ".curry/pakcs-3.2.0/N.icurry", start = Position {file = ".curry/pakcs-3.2.0/N.icurry", line = 3, column = 7}, end = Position {file = ".curry/pakcs-3.2.0/N.icurry", line = 3, column = 15}}, srcInfoPoints = []}, qidModule = Just (ModuleIdent {midSpanInfo = SpanInfo {srcSpan = Span {file = ".curry/pakcs-3.2.0/N.icurry", start = Position {file = ".curry/pakcs-3.2.0/N.icurry", line = 3, column = 7}, end = Position {file = ".curry/pakcs-3.2.0/N.icurry", line = 3, column = 8}}, srcInfoPoints = []}, midQualifiers = ["M"]}), qidIdent = Ident {idSpanInfo = SpanInfo {srcSpan = Span {file = ".curry/pakcs-3.2.0/N.icurry", start = Position {file = ".curry/pakcs-3.2.0/N.icurry", line = 4, column = 3}, end = Position {file = ".curry/pakcs-3.2.0/N.icurry", line = 4, column = 9}}, srcInfoPoints = [Span {file = ".curry/pakcs-3.2.0/N.icurry", start = Position {file = ".curry/pakcs-3.2.0/N.icurry", line = 4, column = 3}, end = Position {file = ".curry/pakcs-3.2.0/N.icurry", line = 4, column = 9}}]}, idName = "methodC", idUnique = 0}}
CallStack (from HasCallStack):
  error, called at src/Base/Messages.hs:78:21 in curry-frontend-2.0.0-2OM1MZb8aCM4fBMC351o4R:Base.Messages
ERROR occurred during parsing!

Interestingly, if we skip module N, but change M to export class C without methodC (as seen in the modified modules below), then methodC is in scope in O, so O compiles without problems. This is probably not intended. At any rate, it is different than the behavior of the GHC, which reports Variable not in scope errors for both the unmodified and modified versions of the modules M, N, and O.

module M (C) where

class C a where
  methodC :: a

module O where

import M

f :: C a => a
f = methodC