SOURCE_FILE
  FN
    FN_KW "fn"
    WHITESPACE " "
    NAME
      IDENT "main"
    PARAM_LIST
      L_PAREN "("
      R_PAREN ")"
    WHITESPACE " "
    BLOCK_EXPR
      STMT_LIST
        L_CURLY "{"
        WHITESPACE " "
        LET_STMT
          LET_KW "let"
          WHITESPACE " "
          IDENT_PAT
            NAME
              IDENT "cl"
          WHITESPACE " "
          EQ "="
          WHITESPACE " "
          CLOSURE_EXPR
            CONST_KW "const"
            WHITESPACE " "
            PARAM_LIST
              PIPE "|"
              PIPE "|"
            WHITESPACE " "
            BIN_EXPR
              UNDERSCORE_EXPR
                UNDERSCORE "_"
              WHITESPACE " "
              EQ "="
              WHITESPACE " "
              LITERAL
                INT_NUMBER "0"
          SEMICOLON ";"
        WHITESPACE " "
        R_CURLY "}"
  WHITESPACE "\n"