[parenscript-devel] four patches to PS-LOOP etc.

[Boris Smilga]

Dear parenscript-devel,

please find attached three patches to the implementation of looping
constructs in Parenscript.  The first provides a more complete support
for CL-LOOP conditional clauses, so that it becomes possible to write,
e. g.:

  (loop for i :from 0 :to 5
        for x := (foo i)
        when x
          collect x
          and if (oddp x)
            collect (1+ x)
          else
            collect (/ x 2)
          end
          and do (alert x))

The second patch implements WITH clauses with implicit initialization
(though not with TYPE-SPECs), e. g.

  (loop for i :from 0 :to 5
        with x
        unless (foo i)
          do (return (setf x i)))

Formerly, this produced incorrect code, because PS-LOOP required
explicit initialization of such variables, but failed to properly
assert that the entity following the variable name is the keyword := .

The third patch implements NAMED and RETURN clauses. Also, it fixes
the problem that PS-LOOP (contrary to CL-LOOP) did not establish an
implicit BLOCK, which used to cause "Returning from unknown block
nilBlock" warnings when RETURN forms were used inside LOOPs.

The fourth patch fixes fallacious generated returns in JavaScript code
where RETURN or RETURN-FROM are used inside conditional expressions
inside loops, as in:

  (block nil
    (dotimes (i 10)
      (if (test i) (return i)))
    (return -1))

This produced the following JavaScript:

  (function () {
      var loopResultVar1 = null;
      for (var i = 0; i < 10; i += 1) {
          if (test(i)) {
              loopResultVar1 = i;
              break;
          };
      };
      return loopResultVar1;
      return -1;
  })();

If test() fails for all values of i, this code evaluates to null.  The
meaning of the original code, however, is for the expression to
evaluate to -1.

So it goes.
Yours,
 — B. Smilga.
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