Parser Animation

e.g. Byacc grammar to input simple infix expressions (without using a Flex):

%%
line    : exp '=' '\n'
        ;
exp     : term | exp '+' term | exp '-' term
        ;
term    : factor | term '*' factor | term '/' factor
	;
factor  : number | '(' exp ')'
	;
number	: digit | number digit
	;
digit	: '0' | '1' | '2' | '3' | '4' | '5' | '6' | '7' | '8' | '9'
	;

given the input line:

1+2=

Roskind's modification to Byacc produces the following:

        .... look ahead at '1'   `1'
'1' <-- `1'
digit
number
|                 .... look ahead at '+'   `+'
factor
term
exp
|       '+' <-- `+'
|       |                 .... look ahead at '2'   `2'
|       |       '2' <-- `2'
|       |       digit
|       |       number
|       |       |                 .... look ahead at '='   `='
|       |       factor
|       |       term
+-------+-------+
|
exp
|       '=' <-- `='
|       |                 .... look ahead at '\n'   `
'
|       |       '\n' <-- `
'
+-------+-------+
|
line
|                 .... look ahead at end-of-file   `'