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js-on-sx: switch/case/default/break

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Parser: jp-parse-switch-stmt + jp-parse-switch-cases + jp-parse-switch-body.
AST: (js-switch discr (("case" val body) ("default" nil body) ...)).

Transpile: wraps body in (call/cc (fn (__break__) ...)). Each case
clause becomes (when (or __matched__ (js-strict-eq discr val))
(set! __matched__ true) body). Fall-through works naturally via
__matched__. Default appended as (when (not __matched__) body).

363/365 unit (+6), 148/148 slice unchanged.
This commit is contained in:
giles
2026-04-23 21:04:22 +00:00
parent 275d2ecbae
commit 9d3e54029a
4 changed files with 167 additions and 0 deletions
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85
lib/js/transpile.sx
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@@ -105,6 +105,8 @@
(js-transpile-postfix (nth ast 1) (nth ast 2)))
((js-tag? ast "js-prefix")
(js-transpile-prefix (nth ast 1) (nth ast 2)))
((js-tag? ast "js-switch")
(js-transpile-switch (nth ast 1) (nth ast 2)))
((js-tag? ast "js-new")
(js-transpile-new (nth ast 1) (nth ast 2)))
((js-tag? ast "js-class")
@@ -558,6 +560,89 @@
(js-sym "__js_old__"))))
(else (error "js-transpile-postfix: unsupported target"))))))
(define
js-transpile-switch
(fn
(discr cases)
(let
((discr-sym (js-sym "__discr__"))
(matched-sym (js-sym "__matched__"))
(break-sym (js-sym "__break__")))
(list
(js-sym "call/cc")
(list
(js-sym "fn")
(list break-sym)
(list
(js-sym "let")
(list
(list discr-sym (js-transpile discr))
(list matched-sym false))
(js-transpile-switch-clauses cases discr-sym matched-sym)))))))
(define
js-transpile-switch-clauses
(fn
(cases discr-sym matched-sym)
(let
((forms (list)))
(for-each
(fn
(c)
(let
((kind (nth c 0)))
(cond
((= kind "case")
(let
((val (nth c 1)) (body (nth c 2)))
(append!
forms
(list
(js-sym "when")
(list
(js-sym "or")
matched-sym
(list
(js-sym "js-strict-eq")
discr-sym
(js-transpile val)))
(js-transpile-switch-body-block matched-sym body)))))
((= kind "default")
(let
((body (nth c 2)))
(append!
forms
(list
(js-sym "when")
matched-sym
(js-transpile-switch-body-block matched-sym body))))))))
cases)
(let
((def-body nil))
(for-each
(fn
(c)
(when (= (nth c 0) "default") (set! def-body (nth c 2))))
cases)
(when
(not (= def-body nil))
(append!
forms
(list
(js-sym "when")
(list (js-sym "not") matched-sym)
(js-transpile-switch-body-block matched-sym def-body)))))
(cons (js-sym "begin") forms))))
(define
js-transpile-switch-body-block
(fn
(matched-sym body)
(let
((forms (list (list (js-sym "set!") matched-sym true))))
(for-each (fn (stmt) (append! forms (js-transpile stmt))) body)
(cons (js-sym "begin") forms))))
(define
js-param-sym
(fn