SOURCE_FILE
  FN
    FN_KW "fn"
    WHITESPACE " "
    NAME
      IDENT "foo"
    PARAM_LIST
      L_PAREN "("
      R_PAREN ")"
    WHITESPACE " "
    BLOCK_EXPR
      STMT_LIST
        L_CURLY "{"
        WHITESPACE "\n    "
        EXPR_STMT
          BECOME_EXPR
            BECOME_KW "become"
            WHITESPACE " "
            CALL_EXPR
              PATH_EXPR
                PATH
                  PATH_SEGMENT
                    NAME_REF
                      IDENT "foo"
              ARG_LIST
                L_PAREN "("
                R_PAREN ")"
          SEMICOLON ";"
        WHITESPACE "\n"
        R_CURLY "}"
  WHITESPACE "\n"
