Discuss an example of handling operator priorities e.g.
%token NUM %left '-' '+' %left '*' '/' %left NEG /* phantom lexeme: unary minus */ %right '^' /* exponentiation */ %% exp: NUM { $$ = $1; } | exp '+' exp { $$ = $1 + $3; } | exp '-' exp { $$ = $1 - $3; } | exp '*' exp { $$ = $1 * $3; } | exp '/' exp { $$ = $1 / $3; } | '-' exp %prec NEG { $$ = -$2; } | exp '^' exp { $$ = pow ($1,$3);} | '(' exp ')' { $$ = $2; } ; %%
Discuss an example of error handling, e.g.
exp: NUM { $$ = $1; } | exp '+' exp { $$ = $1 + $3; } | exp '-' exp { $$ = $1 - $3; } | exp '*' exp { $$ = $1 * $3; } | exp '/' exp { $$ = $1 / $3; } | '-' exp %prec NEG { $$ = -$2; } | exp '^' exp { $$ = pow ($1,$3);} | '(' exp ')' { $$ = $2; } | '(' error ')' { printf("Error in expression\n");$$ = 0;} ;
The students should implement above examples in their code; apart from that thay write their Latte parsers.
Priorities:
precedence left PLUS, MINUS; precedence left TIMES, DIVIDE, MOD; precedence left UMINUS; expr ::= MINUS expr:e {: RESULT = new Integer(0 - e.intValue()); :} %prec UMINUS
Error handling:
stmt ::= expr SEMI | while_stmt SEMI | if_stmt SEMI | ... | error SEMI ;
Similar to Bison, e.g.
%left '+' '-'
%left '*' '/'
%left NEG
%%
Exp :
| Exp '+' Exp { Plus $1 $3 }
| Exp '-' Exp { Minus $1 $3 }
| Exp '*' Exp { Times $1 $3 }
| Exp '/' Exp { Div $1 $3 }
| '(' Exp ')' { Brack $2 }
| '-' Exp %prec NEG { Negate $2 }
| int { Int $1 }Discuss an example, e.g.
entrypoints Exp; EAdd. Exp ::= Exp "+" Exp1 ; EMul. Exp1 ::= Exp1 "*" Exp2 ; ENum. Exp2 ::= Integer ; coercions Exp 2;
Students should