collections/string-operator.cfa:277:1 error: Cannot choose between 4 alternatives for expression
Applying untyped:
  Name: ?|?
...to:
  Name: sout
  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, 1, 0, 0, 1, -2, 0 ): Application of
      Variable Expression: ?|?: forall
        instance of type ostype (not function type)
        with assertions
        Variable Expression: basic_ostream_table: reference to const instance of struct basic_ostream_data with body
        ... with parameters
          instance of type ostype (not function type)

        ... with resolved type:
          reference to const instance of struct basic_ostream_data with body
          ... with parameters
            instance of type ostype (not function type)

        function
      ... with parameters
        reference to instance of type ostype (not function type)
        char
      ... returning
        reference to instance of type ostype (not function type)

      ... with resolved type:
        pointer to forall
          instance of type [unbound] (not function type)
          with assertions
          Variable Expression: basic_ostream_table: reference to const instance of struct basic_ostream_data with body
          ... with parameters
            instance of type ostype (not function type)

          ... with resolved type:
            reference to const instance of struct basic_ostream_data with body
            ... with parameters
              instance of type [unbound] (not function type)

          function
        ... with parameters
          reference to instance of type [unbound] (not function type)
          char
        ... returning
          reference to instance of type [unbound] (not function type)

      ... to arguments
      Variable Expression: sout: extern reference to instance of struct ofstream with body
      ... with resolved type:
        reference to instance of struct ofstream 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 inferred parameters 0:
      basic_ostream_table: extern reference to const instance of struct basic_ostream_data with body
      ... with parameters
        instance of struct ofstream with body


    ... with resolved type:
      reference to instance of type [unbound] (not function type)
  (types:
    reference to instance of type [unbound] (not function type)
  )
  Environment:([unbound]ostype) -> instance of struct ofstream with body (no widening)


Cost ( 0, 0, 1, 0, 0, 1, -2, 0 ): Application of
      Variable Expression: ?|?: forall
        instance of type ostype (not function type)
        with assertions
        Variable Expression: basic_ostream_table: reference to const instance of struct basic_ostream_data with body
        ... with parameters
          instance of type ostype (not function type)

        ... with resolved type:
          reference to const instance of struct basic_ostream_data with body
          ... with parameters
            instance of type ostype (not function type)

        function
      ... with parameters
        reference to instance of type ostype (not function type)
        char
      ... returning nothing

      ... with resolved type:
        pointer to forall
          instance of type [unbound] (not function type)
          with assertions
          Variable Expression: basic_ostream_table: reference to const instance of struct basic_ostream_data with body
          ... with parameters
            instance of type ostype (not function type)

          ... with resolved type:
            reference to const instance of struct basic_ostream_data with body
            ... with parameters
              instance of type [unbound] (not function type)

          function
        ... with parameters
          reference to instance of type [unbound] (not function type)
          char
        ... returning nothing

      ... to arguments
      Variable Expression: sout: extern reference to instance of struct ofstream with body
      ... with resolved type:
        reference to instance of struct ofstream 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 inferred parameters 0:
      basic_ostream_table: extern reference to const instance of struct basic_ostream_data with body
      ... with parameters
        instance of struct ofstream with body


    ... with resolved type:
      void
  (types:
    void
  )
  Environment:([unbound]ostype) -> instance of struct ofstream with body (no widening)


Cost ( 0, 0, 1, 0, 0, 1, -2, 0 ): Application of
      Variable Expression: ?|?: forall
        instance of type ostype (not function type)
        with assertions
        Variable Expression: basic_ostream_table: reference to const instance of struct basic_ostream_data with body
        ... with parameters
          instance of type ostype (not function type)

        ... with resolved type:
          reference to const instance of struct basic_ostream_data with body
          ... with parameters
            instance of type ostype (not function type)

        function
      ... with parameters
        reference to instance of type ostype (not function type)
        instance of struct string with body
      ... returning
        reference to instance of type ostype (not function type)

      ... with resolved type:
        pointer to forall
          instance of type [unbound] (not function type)
          with assertions
          Variable Expression: basic_ostream_table: reference to const instance of struct basic_ostream_data with body
          ... with parameters
            instance of type ostype (not function type)

          ... with resolved type:
            reference to const instance of struct basic_ostream_data with body
            ... with parameters
              instance of type [unbound] (not function type)

          function
        ... with parameters
          reference to instance of type [unbound] (not function type)
          instance of struct string with body
        ... returning
          reference to instance of type [unbound] (not function type)

      ... to arguments
      Variable Expression: sout: extern reference to instance of struct ofstream with body
      ... with resolved type:
        reference to instance of struct ofstream 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 inferred parameters 0:
      basic_ostream_table: extern reference to const instance of struct basic_ostream_data with body
      ... with parameters
        instance of struct ofstream with body


    ... with resolved type:
      reference to instance of type [unbound] (not function type)
  (types:
    reference to instance of type [unbound] (not function type)
  )
  Environment:([unbound]ostype) -> instance of struct ofstream with body (no widening)


Cost ( 0, 0, 1, 0, 0, 1, -2, 0 ): Application of
      Variable Expression: ?|?: forall
        instance of type ostype (not function type)
        with assertions
        Variable Expression: basic_ostream_table: reference to const instance of struct basic_ostream_data with body
        ... with parameters
          instance of type ostype (not function type)

        ... with resolved type:
          reference to const instance of struct basic_ostream_data with body
          ... with parameters
            instance of type ostype (not function type)

        function
      ... with parameters
        reference to instance of type ostype (not function type)
        instance of struct string with body
      ... returning nothing

      ... with resolved type:
        pointer to forall
          instance of type [unbound] (not function type)
          with assertions
          Variable Expression: basic_ostream_table: reference to const instance of struct basic_ostream_data with body
          ... with parameters
            instance of type ostype (not function type)

          ... with resolved type:
            reference to const instance of struct basic_ostream_data with body
            ... with parameters
              instance of type [unbound] (not function type)

          function
        ... with parameters
          reference to instance of type [unbound] (not function type)
          instance of struct string with body
        ... returning nothing

      ... to arguments
      Variable Expression: sout: extern reference to instance of struct ofstream with body
      ... with resolved type:
        reference to instance of struct ofstream 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 inferred parameters 0:
      basic_ostream_table: extern reference to const instance of struct basic_ostream_data with body
      ... with parameters
        instance of struct ofstream with body


    ... with resolved type:
      void
  (types:
    void
  )
  Environment:([unbound]ostype) -> instance of struct ofstream with body (no widening)