ref: 74bd921fc755aefb20c8171d83758bc3f5d0877b
dir: /examples/dcv.peg/
# Grammar
Stmt <- SPACE Expr EOL { printf("%d\n", pop()); }
/ (!EOL .)* EOL { printf("error\n"); }
Expr <- ID { var= yytext[0] } ASSIGN Sum { vars[var - 'a']= top(); }
/ Sum
Sum <- Product ( PLUS Product { int r= pop(), l= pop(); push(l + r); }
/ MINUS Product { int r= pop(), l= pop(); push(l - r); }
)*
Product <- Value ( TIMES Value { int r= pop(), l= pop(); push(l * r); }
/ DIVIDE Value { int r= pop(), l= pop(); push(l / r); }
)*
Value <- NUMBER { push(atoi(yytext)); }
/ < ID > !ASSIGN { push(vars[yytext[0] - 'a']); }
/ OPEN Expr CLOSE
# Lexemes
NUMBER <- < [0-9]+ > SPACE
ID <- < [a-z] > SPACE
ASSIGN <- '=' SPACE
PLUS <- '+' SPACE
MINUS <- '-' SPACE
TIMES <- '*' SPACE
DIVIDE <- '/' SPACE
OPEN <- '(' SPACE
CLOSE <- ')' SPACE
SPACE <- [ \t]*
EOL <- '\n' / '\r\n' / '\r' / ';'