Type equality modulo type distinction

The following algorithm (in pseudo-code) determines whether two types are equal with no respect to distinct types. For brevity the cycle check with an auxiliary set s is omitted:

proc typeEqualsOrDistinct(a, b: PType): bool =
  if a.kind == b.kind:
    case a.kind
    of int, intXX, float, floatXX, char, string, cstring, pointer,
        bool, nil, void:
      # leaf type: kinds identical; nothing more to check
      result = true
    of ref, ptr, var, set, seq, openarray:
      result = typeEqualsOrDistinct(a.baseType, b.baseType)
    of range:
      result = typeEqualsOrDistinct(a.baseType, b.baseType) and
        (a.rangeA == b.rangeA) and (a.rangeB == b.rangeB)
    of array:
      result = typeEqualsOrDistinct(a.baseType, b.baseType) and
               typeEqualsOrDistinct(a.indexType, b.indexType)
    of tuple:
      if a.tupleLen == b.tupleLen:
        for i in 0..a.tupleLen-1:
          if not typeEqualsOrDistinct(a[i], b[i]): return false
        result = true
    of distinct:
      result = typeEqualsOrDistinct(a.baseType, b.baseType)
    of object, enum:
      result = a == b
    of proc:
      result = typeEqualsOrDistinct(a.parameterTuple, b.parameterTuple) and
               typeEqualsOrDistinct(a.resultType, b.resultType) and
               a.callingConvention == b.callingConvention
  elif a.kind == distinct:
    result = typeEqualsOrDistinct(a.baseType, b)
  elif b.kind == distinct:
    result = typeEqualsOrDistinct(a, b.baseType)