grammar.y

用YACC实现的一个小的编译工具

%start ROOT

%token EQ
%token NE
%token LT
%token LE
%token GT
%token GE
%token PLUS
%token MINUS
%token MULT
%token DIVIDE
%token RPAREN
%token LPAREN
%token ASSIGN
%token SEMICOLON
%token IF
%token THEN
%token ELSE
%token FI
%token WHILE
%token DO
%token OD
%token PRINT
%token NUMBER
%token NAME

%%

ROOT:
  stmtseq { execute($1); } 
;

statement:
  designator ASSIGN expression { $$ = assignment($1, $3); } 
| PRINT expression { $$ = print($2); } 
| IF expression THEN stmtseq ELSE stmtseq FI { $$ = ifstmt($2, $4, $6); }
| IF expression THEN stmtseq FI { $$ = ifstmt($2, $4, empty()); }
| WHILE expression DO stmtseq OD { $$ = whilestmt($2, $4); }
;

stmtseq:
  stmtseq SEMICOLON statement { $$ = seq($1, $3); }
| statement { $$ = $1; }
;

expression:
  expr2 { $$ = $1; } 
| expr2 EQ expr2 { $$ = eq($1, $3); }
| expr2 NE expr2 { $$ = ne($1, $3); }
| expr2 LT expr2 { $$ = le($1, $3); }
| expr2 LE expr2 { $$ = le($1, $3); }
| expr2 GT expr2 { $$ = gt($1, $3); }
| expr2 GE expr2 { $$ = gt($1, $3); }
;

expr2:
  expr3 { $$ == $1; }
| expr2 PLUS expr3 { $$ = plus($1, $3); }
| expr2 MINUS expr3 { $$ = minus($1, $3); }
;

expr3:
  expr4 { $$ = $1; }
| expr3 MULT expr4 { $$ = mult($1, $3); }
| expr3 DIVIDE expr4 { $$ = divide ($1, $3); }
;

expr4:
  PLUS expr4 { $$ = $2; }
| MINUS expr4 { $$ = neg($2); }
| LPAREN expression RPAREN { $$ = $2; }
| NUMBER { $$ = number($1); }
| designator { $$ = $1; }
;

designator:
  NAME { $$ = name($1); }
;