javascript - 向JISON添加声明

我这里仅是JISON计算器示例的略微修改版本:

/* description: Parses end 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

%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
        {$$ = Math.pow($1, $3);}
    | e '!'
        {{
          $$ = fact($1);
        }}
    | e '%'
        {$$ = $1/100;}
    | '-' e %prec UMINUS
        {$$ = -$2;}
    | '(' e ')'
        {$$ = $2;}
    | NUMBER
        {$$ = Number(yytext);}
    | E
        {$$ = Math.E;}
    | PI
        {$$ = Math.PI;}
    ;

%%
/*why doesn't this work at runtime?
I see other examples defining declarations this way but I must be doing something wrong
I couldn't find a syntactically valid way of putting this declaration anywhere but here,
which is probably the issue*/
function fact(n) {
  var tot=1;
  for(var i=2;i<=n;++i) {
    tot*=i;
  }
  return tot;
}

注意!运算符的定义略有不同。我正在尝试从外部定义fact函数，而不是内联。

到目前为止，它在运行时告诉我fact is not defined。我怎样才能解决这个问题？另外，为什么计算器示例在阶乘定义{{ /*like so*/ }}周围使用两个大括号？

最佳答案

要调用在生产环境下定义的函数(例如fact)，可以对多行​​语义 Action 使用mod-brace表示法%{和%}:

e
    : e '+' e

    ...

    | e '!'
        %{
            // the %{ tells jison this is a multi-line js eval statement
            $$ = fact($1);
        %}
    ;

作为最终解决方案，请尝试以下操作:

/* 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

%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
        {$$ = Math.pow($1, $3);}
    | e '!'
        %{
          $$ = fact($1);
        %}
    | e '%'
        {$$ = $1/100;}
    | '-' e %prec UMINUS
        {$$ = -$2;}
    | '(' e ')'
        {$$ = $2;}
    | NUMBER
        {$$ = Number(yytext);}
    | E
        {$$ = Math.E;}
    | PI
        {$$ = Math.PI;}
    ;

%%

function fact(n) {
  var tot=1;
  for(var i=2;i<=n;++i) {
    tot*=i;
  }
  return tot;
}

关于javascript - 向JISON添加声明，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/14528648/