September 2010 - parenscript-devel - mailman3.common-lisp.net

[parenscript-devel] Patch: added JS label/break to PS
by Daniel Gackle 07 Dec '10

07 Dec '10

I just pushed a patch (authored by Scott) to implement JS's LABEL and BREAK in PS. (Note that this patch deprecates LABELED-FOR since you can get the same effect by combining LABEL and FOR. Was anybody using LABELED-FOR?) Here's an example: (label scope (foo) (when (bar) (break scope)) (blee)) => scope: { foo(); if (bar()) { break scope; }; blee(); }; I was astonished to discover recently that JS has supported this ability all along in the form of labeled statements and labeled breaks. I'd always assumed that to get explicit returns from an arbitrary scope, you'd have to resort to the ugly hack of muscling TRY/CATCH to do it, thinking that this was the closest JS counterpart. (See http://news.ycombinator.com/item?id=793092 for a thread in which several people believe this.) But it appears we were all wrong. What's not clear yet is how far this can be taken. Can you use it inside a nested local function to return immediately from the top-level function? That is one thing I've wanted for a long time. In the ideal case, LABEL/BREAK could be used as a base for implementing a proper BLOCK and RETURN-FROM in PS, something which we'd long believed to be impossible. One challenge is that in CL, RETURN-FROM can take a value, which becomes the value of BLOCK. In other words, BLOCK in CL is an expression while LABEL in JS is not. It seems, though, that most of this challenge has already been conquered with the development of implicit return in PS. The only thing you'd need to add is detecting when BLOCK is being used as an expression, declaring a gensymed variable and assigning whatever is happening inside BLOCK to that variable (much like implicit return already does with e.g. CASE), then put the variable in the expression position that BLOCK was in. It seems like this ought to work. It would also make things like this possible in PS: (1+ (case foo (:eleven 11) (:twelve 12))) Vladimir (and everybody), is the above clear? What do you think of it? Daniel

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[parenscript-devel] in-package and Parenscript compilation
by Alessio Stalla 06 Nov '10

06 Nov '10

Greetings, I'm approaching Parenscript and I must say I'm really impressed by this library. Kudos to the developers! But I find one thing missing: the Parenscript stream/file compiler does not understand in-package forms like the CL file compiler does; rather, it reads all the forms in the package which is current at the time it gets called. This makes it slightly inconvenient to compile Lisp files which need to be read in a certain package, and completely impossible to handle files which change *package* mid-file (which is generally not a good idea, but still it's possible in CL). I'm attaching a patch against src/compilation-interface.lisp to make the compiler behave like the CL one; comments are welcome. Regards, Alessio Stalla

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[parenscript-devel] Parenscript condition system implemented for PSOS
by Red Daly 01 Oct '10

01 Oct '10

I have added a Common Lisp-like condition system to the Parenscript Object System (PSOS). Parenscript now has HANDLER-BIND, HANDLER-CASE, RESTART-CASE, RESTART-BIND, INVOKE-RESTART, and SIGNAL. The patch that adds this is here: http://github.com/gonzojive/paren-psos/commit/6578ad223515dc2c1ddf49346f4ba… and totals about 200 lines, plus 200 lines of test cases. It could probably work without a type system at all, but it will require some runtime code no matter what. The whole PSOS system is backed by a test suite that uses CL-Spidermonkey. Take a look at PSOS here: http://github.com/gonzojive/paren-psos for more details. Enjoy! Red

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