parse(input: &str) -> Expression { let mut tokens = tokenize(input); fn parse_expr<'a>(tokens: &mut Tokenizer<'a>) -> Expression { let Some(tok) = tokens.next() else { panic!("Unexpected end of input"); }; // バイナリ演算が存在する場合はパースします。 match tokens.next() { None => expr, Some(Token::Operator(op)) => Expression::Operation( Box::new(expr), op, Box::new(parse_expr(tokens)), ), Some(tok) => panic!("Unexpected ("Unexpected token {tok:?}"), } } parse_expr(&mut tokens) } fn main() { let expr = parse("10+foo+20-30"); println!("{expr:?}"); } 29.8.1 解答 use thiserror::Error; use std::iter::Peekable; use std::str::Chars;

( and ) ) to define clauses of related tokens and values. Parentheses must always be matched: for every ( there must be a matching ) . Inside a clause, tokens and values are separated by whitespace whitespace. By convention, a single space is used, but any number of whitespace characters between tokens is acceptable. In places where text strings are valid, strings without any whitespace may be quoted with syntax descriptions below, items in represent tokens that must be present and items in [square brackets] represent tokens that are optional or only sometimes required. The Custom Rules

bison */ %{ #include extern int yylex(void); extern int yyerror(char *); %} /* declare tokens */ %token NUMBER %token OP_ADD OP_SUB OP_MUL OP_RGT OP_LFT OP_EQU %% calc: | calc exp OP_EQU {

用のスクリプトの例を次に示します。このスクリプトでは各 ファイルに異なる名前を付けるために、タイムスタンプ・サフィックスを 使用します (USERNAME を実際のユーザ名に置き換えます)。 @echo off for /f "tokens=2 delims==" %%a in ('wmic OS Get localdatetime /value') do set "dt=%%a" set "YY=%dt:~2,2%" & set