[parenscript-devel] 'use strict' and 'with' in loop

[Peter Wood]

Hi

It's my first post, so first of all, thanks to everyone who works on
parenscript.  It is a lifesaver.

If I 'use strict'; in the start of my scripts, they fail in some of the
loops because parenscript is generating a 'with' (which is not allowed in
strict mode).   There is quite a nice explanation of why it isn't allowed
here:

https://developer.mozilla.org/en-US/docs/JavaScript/Reference/Functions_and_function_scope/Strict_mode

It is easy to change my code to use 'do' instead, and for now, that's what
I've done, but it's a shame not to be able to use parenscript's very nice
loop for writing javascript loops.  I haven't looked at parenscript's code
before this evening, but I think this is the relevant spot (in
src/special-operators.lisp)

(defun compile-loop-body
...
(aif (sort (remove-duplicates *loop-scope-lexicals-captured*)
               #'string< :key #'symbol-name)
         `(ps-js:block
              (ps-js:with
                  ,(compile-expression
                    `(create
                      ,@(loop for x in it
                              collect x
                              collect (when (member x loop-vars) x))))
                ,compiled-body))
         compiled-body)))

Here is an example of some lisp and the js which it generates:

(ps:ps (defun foo ()
                  (loop for i from 1 to 5
                     append (loop for j from 1 to 5
                                 collect (list i j)))))
==>
"function foo() {
    return (function () {
        var append9 = [];
        for (var i = 1; i <= 5; i += 1) {
            with ({ i : i }) {
        ^^^^^^^^^^
                append9 = append9.concat((function () {
                    var collect10 = [];
                    for (var j = 1; j <= 5; j += 1) {
                        collect10['push']([i, j]);
                    };
                    return collect10;
                })());
            };
        };
        return append9;
    })();
};"

What is the point of even having the 'with ({ i : i })' in there ??  I have
tried removing the form starting (ps-js:with ... ) and the code which is
then generated runs fine and has no 'with', but of course it is probably
breaking something else.  I don't understand why it's there.

Regards,
Peter
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