parenscript-devel

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December 2022

2 participants
2 discussions

Adding CL:TAGBODY for SERIES support
by Andrew Easton 10 Feb '23

10 Feb '23

Hello everyone, It seems valuable to compile SERIES [1] macros with PARENSCRIPT [2], however, parenscript does not currently seem to support CL:TAGBODY [3,4]. Even poking around the HyperSpec and discovering that CL:DO provides *not* an implicit progn, but an implicit tagbody [5], does not help. The (PARENSCRIPT:DO ...)-form only has an implicit progn around the body [3]. I have started to implement TAGBODY for PARENSCRIPT [A,B,C]. The general idea is to imitate a jump table by looping over a switch-case. A GO (C-terminology: jump) then sets the switch-variable to the next jump destination. The loop subsequently causes the switch to branch to the jump target in the switch-variable. Leaving the tagbody means leaving the loop. There are complications. Common Lisp allows nested tagbody-forms. Common Lisp allows go-tags to be referenced within the lexical scope *and* the dynamic extent of a tagbody form. This means that a LAMBDA can close over a go-tag and jump there, see an example in [B], of how inconvenient this can become for compilation to JavaScript. PARENSCRIPT is well-designed. Its compilation of BLOCKs, LOOPs and SWITCHes seems to permit compilation of a TAGBODY to JavaScript code. PARENSCRIPT even handles RETURNing from a BLOCK via a LAMBDA by automatically creating a JavaScript try-catch. This seems to curb the inconveniences brought on by lexical closures jumping to go-tags in the TAGBODY's dynamic extent. I need help in the following points: 1. I need a code review of the algorithm. The implementation in [B] seems to be satisfactory. There are some test cases and examples. Most there is the most hairy example I could find up to now. I may have missed crucial details. 2. My understanding of the CL:TAGBODY definition in the CLHS [4] may be wrong. Which alternate interpretations does anybody here know of? 3. What examples of PARENSCRIPT:DEFPSMACRO do you know, that might help me understand its semantics? I would hazard a guess at DEFPSMACRO being a facility to add TAGBODY to PARENSCRIPT, however, my understanding of DEFPSMACRO is very bad and I do not know where to start tinkering with it to further my understanding. Kind regards, Andrew Easton === Attachments === [A] 2022-05-20_defmacro-series-expand.lisp [B] 2022-05-20_parenscript-devel_tagbody-code-short.lisp [C] 2022-05-20_parenscript-devel_tagbody-code-long.lisp The long version contains some dead-ends that were encountered during development. This is an important source of counter-examples. === References === [1] The SERIES macro package a. https://www.cs.cmu.edu/Groups/AI/html/cltl/clm/node347.html#SECTION00340000… b. https://www.cs.cmu.edu/Groups/AI/html/cltl/clm/node362.html#SECTION00350000… c. https://dspace.mit.edu/handle/1721.1/6035 d. https://dspace.mit.edu/handle/1721.1/6031 e. (ql:quickload :series) f. https://sourceforge.net/projects/series/ [2] Parenscript https://parenscript.common-lisp.dev/ [3] Parenscript Reference manual (updated 2019-10-15) https://parenscript.common-lisp.dev/reference.html [4] Common Lisp HyperSpec (CLHS) entry for CL:TAGBODY http://www.lispworks.com/documentation/HyperSpec/Body/s_tagbod.htm#tagbody [5] Common Lisp HyperSpec (CLHS) entry for CL:DO http://www.lispworks.com/documentation/HyperSpec/Body/m_do_do.htm#do

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function "at" is undefined
by David O'Toole 14 Dec '22

14 Dec '22

Using the dot syntax for identifiers works (with a warning), but (@ a b) and (getprop a b) don't work, the functions are undefined. What am I doing wrong?

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