SOURCE_FILE
  ERROR
    LET_KW "let"
    WHITESPACE " "
    IDENT_PAT
      REF_KW "ref"
      WHITESPACE " "
      NAME
        IDENT "foo"
    COLON ":"
    WHITESPACE " "
    FN_PTR_TYPE
      FN_KW "fn"
      PARAM_LIST
        L_PAREN "("
        R_PAREN ")"
    WHITESPACE " "
    EQ "="
    WHITESPACE " "
    BIN_EXPR
      LITERAL
        INT_NUMBER "1"
      WHITESPACE " "
      PLUS "+"
      WHITESPACE " "
      LITERAL
        INT_NUMBER "3"
    SEMICOLON ";"
  WHITESPACE "\n"
error 0: expected an item
