Created
April 9, 2017 08:58
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/* description: Parses and executes mathematical expressions. */ | |
/* lexical grammar */ | |
%lex | |
%% | |
\s+ /* skip whitespace */ | |
[0-9]+("."[0-9]+)?\b return 'NUMBER'; | |
"*" return '*'; | |
"/" return '/'; | |
"-" return '-'; | |
"+" return '+'; | |
"^" return '^'; | |
"!" return '!'; | |
"%" return '%'; | |
"(" return '('; | |
")" return ')'; | |
"PI" return 'PI'; | |
"E" return 'E'; | |
<<EOF>> return 'EOF'; | |
. return 'INVALID'; | |
/lex | |
/* operator associations and precedence */ | |
%left '+' '-' | |
%left '*' '/' | |
%left '^' | |
%right '!' | |
%right '%' | |
%left UMINUS | |
%token INVALID | |
%start expressions | |
%% /* language grammar */ | |
expressions | |
: e EOF | |
{ typeof console !== 'undefined' ? console.log($1) : print($1); | |
return $1; } | |
; | |
e | |
: e '+' e | |
{$$ = $1 + $3;} | |
| e '-' e | |
{$$ = $1 - $3;} | |
| e '*' e | |
{$$ = $1 * $3;} | |
| e '/' e | |
{$$ = $1 / $3;} | |
| e '^' e | |
{$$ = Math.pow($1, $3);} | |
| e '!' | |
{{ | |
$$ = (function fact(n) { | |
return n == 0 ? 1 : fact(n - 1) * n; | |
})($1); | |
}} | |
| e '%' | |
{$$ = $1 / 100;} | |
| '-' e %prec UMINUS | |
{$$ = -$2;} | |
| '(' e ')' | |
{$$ = $2;} | |
| NUMBER | |
{$$ = Number(yytext);} | |
| E | |
{$$ = Math.E;} | |
| PI | |
{$$ = Math.PI;} | |
; |
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