ref: 74b7881f93ea9d2df51931debba10770b7fa9cbc
dir: /examples/dc.peg/
# Grammar
Expr <- SPACE Sum EOL { printf("%d\n", pop()); }
/ (!EOL .)* EOL { printf("error\n"); }
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)); }
/ OPEN Sum CLOSE
# Lexemes
NUMBER <- < [0-9]+ > SPACE
PLUS <- '+' SPACE
MINUS <- '-' SPACE
TIMES <- '*' SPACE
DIVIDE <- '/' SPACE
OPEN <- '(' SPACE
CLOSE <- ')' SPACE
SPACE <- [ \t]*
EOL <- '\n' / '\r\n' / '\r'