Re: request for simple example: parse tree generation

>I'm looking for a *simple* example that shows how to generate
>an explicit parse tree using yacc. Since the tool is used a lot,
>I thought there would be some sort of "standard" way of doing this.


>Kendra
>[Yeah, I wanted to put some examples of that in the book, but ran out of
>time and pages. It's pretty straightforward, generate subtrees each time
>you reduce a rule and splice them together as you go, ending up with one
>big tree when the parse is done. -John]


as in the following fragment...
ParseTree(opcode,...) constructs a tree node
Here the stack is used both to pass tree nodes (as in product_expr)
and opcodes (as in product_op).


product_expr
: product_expr product_op cast_expr
{ $$ = ParseTree($2,$1,$3); }
| cast_expr { $$ = $1; }
;


product_op /* miltiplicative_expr */
: '*' { $$ = opMULT; }
| '/' { $$ = opDIV; }
| '%' { $$ = opREM; }
| tkMOD { $$ = opMOD; }
;


conditional_expr /* AC: could be called simple_expr */
: infix_expr { $$ = $1; }
| infix_expr '?' expr ':' conditional_expr
{ $$ = ParseTree(opCONDEXP,$1,$3,$5); }
;


assignment_expr
: conditional_expr { $$ = $1; }
| unary_expr assignment_operator assignment_expr
{ $$ = ParseTree($2,$1,$3); }
;


single_expr /* no commas */
: assignment_expr { $$ = $1; }
;


--
Alex Colvin
alex.colvin@dartmouth.edu


--

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