SOURCE_FILE
  FN
    FN_KW "fn"
    WHITESPACE " "
    NAME
      IDENT "main"
    PARAM_LIST
      L_PAREN "("
      R_PAREN ")"
    WHITESPACE " "
    BLOCK_EXPR
      STMT_LIST
        L_CURLY "{"
        WHITESPACE "\n    "
        LET_STMT
          LET_KW "let"
          WHITESPACE " "
          IDENT_PAT
            NAME
              IDENT "a"
          WHITESPACE " "
          EQ "="
          WHITESPACE " "
          TUPLE_EXPR
            L_PAREN "("
            R_PAREN ")"
          SEMICOLON ";"
        WHITESPACE "\n    "
        LET_STMT
          LET_KW "let"
          WHITESPACE " "
          IDENT_PAT
            MUT_KW "mut"
            WHITESPACE " "
            NAME
              IDENT "b"
          WHITESPACE " "
          EQ "="
          WHITESPACE " "
          TUPLE_EXPR
            L_PAREN "("
            R_PAREN ")"
          SEMICOLON ";"
        WHITESPACE "\n    "
        LET_STMT
          LET_KW "let"
          WHITESPACE " "
          IDENT_PAT
            REF_KW "ref"
            WHITESPACE " "
            NAME
              IDENT "c"
          WHITESPACE " "
          EQ "="
          WHITESPACE " "
          TUPLE_EXPR
            L_PAREN "("
            R_PAREN ")"
          SEMICOLON ";"
        WHITESPACE "\n    "
        LET_STMT
          LET_KW "let"
          WHITESPACE " "
          IDENT_PAT
            REF_KW "ref"
            WHITESPACE " "
            MUT_KW "mut"
            WHITESPACE " "
            NAME
              IDENT "d"
          WHITESPACE " "
          EQ "="
          WHITESPACE " "
          TUPLE_EXPR
            L_PAREN "("
            R_PAREN ")"
          SEMICOLON ";"
        WHITESPACE "\n    "
        LET_STMT
          LET_KW "let"
          WHITESPACE " "
          IDENT_PAT
            NAME
              IDENT "e"
            WHITESPACE " "
            AT "@"
            WHITESPACE " "
            WILDCARD_PAT
              UNDERSCORE "_"
          WHITESPACE " "
          EQ "="
          WHITESPACE " "
          TUPLE_EXPR
            L_PAREN "("
            R_PAREN ")"
          SEMICOLON ";"
        WHITESPACE "\n    "
        LET_STMT
          LET_KW "let"
          WHITESPACE " "
          IDENT_PAT
            REF_KW "ref"
            WHITESPACE " "
            MUT_KW "mut"
            WHITESPACE " "
            NAME
              IDENT "f"
            WHITESPACE " "
            AT "@"
            WHITESPACE " "
            IDENT_PAT
              NAME
                IDENT "g"
              WHITESPACE " "
              AT "@"
              WHITESPACE " "
              WILDCARD_PAT
                UNDERSCORE "_"
          WHITESPACE " "
          EQ "="
          WHITESPACE " "
          TUPLE_EXPR
            L_PAREN "("
            R_PAREN ")"
          SEMICOLON ";"
        WHITESPACE "\n"
        R_CURLY "}"
  WHITESPACE "\n"
