collections/string-operator.cfa:139:1 error: Cannot choose between 2 alternatives for expression
Applying untyped:
  Name: ?{}
...to:
  Generated Cast of:
    Variable Expression: s: instance of struct string with body
    ... with resolved type:
      instance of struct string with body
  ... to:
    reference to instance of struct string with body
  ... with resolved type:
    reference to instance of struct string with body
  Applying untyped:
    Name: ?+?
  ...to:
    Constant Expression ('a': char)
    ... with resolved type:
      char
    Constant Expression ('b': char)
    ... with resolved type:
      char

 Alternatives are:
Cost ( 0, 0, 0, 0, 0, 0, 0, 1 ): Application of
      Variable Expression: ?{}: function
      ... with parameters
        reference to instance of struct string with body
        char
      ... returning nothing

      ... with resolved type:
        pointer to function
        ... with parameters
          reference to instance of struct string with body
          char
        ... returning nothing

      ... to arguments
      Generated Cast of:
        Variable Expression: s: instance of struct string with body
        ... with resolved type:
          instance of struct string with body
      ... to:
        reference to instance of struct string with body
      ... with resolved type:
        reference to instance of struct string with body
      Application of
        Variable Expression: ?+?: function
        ... with parameters
          char
          char
        ... returning
          char

        ... with resolved type:
          pointer to function
          ... with parameters
            char
            char
          ... returning
            char

        ... to arguments
        Constant Expression ('a': char)
        ... with resolved type:
          char
        Constant Expression ('b': char)
        ... with resolved type:
          char

      ... with resolved type:
        char

    ... with resolved type:
      void
  (types:
    void
  )
  Environment:

Cost ( 0, 0, 0, 0, 0, 0, 0, 1 ): Application of
      Variable Expression: ?{}: function
      ... with parameters
        reference to instance of struct string with body
        instance of struct string with body
      ... returning nothing

      ... with resolved type:
        pointer to function
        ... with parameters
          reference to instance of struct string with body
          instance of struct string with body
        ... returning nothing

      ... to arguments
      Generated Cast of:
        Variable Expression: s: instance of struct string with body
        ... with resolved type:
          instance of struct string with body
      ... to:
        reference to instance of struct string with body
      ... with resolved type:
        reference to instance of struct string with body
      Application of
        Variable Expression: ?+?: function
        ... with parameters
          char
          char
        ... returning
          instance of struct string with body

        ... with resolved type:
          pointer to function
          ... with parameters
            char
            char
          ... returning
            instance of struct string with body

        ... to arguments
        Constant Expression ('a': char)
        ... with resolved type:
          char
        Constant Expression ('b': char)
        ... with resolved type:
          char

      ... with resolved type:
        instance of struct string with body

    ... with resolved type:
      void
  (types:
    void
  )
  Environment:


collections/string-operator.cfa:139:1 error: No alternatives for expression Name: s
