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evaluator: recur into a variadic arity binds the rest seq directly (fixes the hang)

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(recur (inc acc) (rest xs)) re-entered the fn through its varargs collector,
so the rest seq came back wrapped in a fresh 1-element rest list — xs never
emptied and the interpreter hung (jolt-4df; the compile path was already
correct). recur now re-enters through a dedicated entry that binds the LAST
arg directly as the rest param (n-fixed + 1 args, Clojure's contract), in
both the single-arity and multi-arity fn* paths; the shared body runner keeps
the ns-swap/restore in one place, and fixed arities still re-dispatch through
the arity dispatcher exactly as before.

Six spec rows: the original repro, zero-fixed variadic, rest-empties-to-nil,
multi-arity variadic recur, nil rest, and a fixed-arity control.
This commit is contained in:
Yogthos 2026-06-10 18:23:10 -04:00
parent 4a4f658f97
commit 502eabdb2d
2 changed files with 84 additions and 23 deletions
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88
src/jolt/evaluator.janet
View file

@ -1407,16 +1407,16 @@
fixed-pats (param-info :fixed)
rest-pat (param-info :rest)
n-fixed (length fixed-pats)
f (fn [& fn-args]
(var fn-bindings @{})
(table/setproto fn-bindings bindings)
(var i 0)
(each pat fixed-pats
(destructure-bind ctx fn-bindings pat (fn-args i))
(++ i))
(when rest-pat
(destructure-bind ctx fn-bindings rest-pat (tuple/slice fn-args i)))
(put fn-bindings :jolt/loop-fn self)
# recur-entry: where (recur ...) re-enters THIS arity. For
# a fixed arity it's the dispatcher (exact count re-selects
# it). For the VARIADIC arity, recur takes n-fixed + 1 args
# with the LAST bound DIRECTLY as the rest seq (Clojure) —
# re-entering through the varargs collector would wrap it
# in a fresh 1-element rest list and the seq never empties
# (the jolt-4df hang).
recur-entry-box @[nil]
run-clause (fn [fn-bindings]
(put fn-bindings :jolt/loop-fn (in recur-entry-box 0))
(when fn-name (bind-put fn-bindings fn-name self))
# Use defining namespace for symbol resolution
(def saved-ns (ctx-current-ns ctx))
@ -1429,10 +1429,33 @@
(each body-form body
(set result (eval-form ctx fn-bindings body-form)))
(ctx-set-current-ns ctx saved-ns)
result)]
result)
f (fn [& fn-args]
(var fn-bindings @{})
(table/setproto fn-bindings bindings)
(var i 0)
(each pat fixed-pats
(destructure-bind ctx fn-bindings pat (fn-args i))
(++ i))
(when rest-pat
(destructure-bind ctx fn-bindings rest-pat (tuple/slice fn-args i)))
(run-clause fn-bindings))]
(if rest-pat
(do (set variadic-fn f) (set variadic-min n-fixed))
(put arities n-fixed f))))
(do
(put recur-entry-box 0
(fn [& recur-args]
(var fn-bindings @{})
(table/setproto fn-bindings bindings)
(var i 0)
(each pat fixed-pats
(destructure-bind ctx fn-bindings pat (recur-args i))
(++ i))
(destructure-bind ctx fn-bindings rest-pat (get recur-args i))
(run-clause fn-bindings)))
(set variadic-fn f) (set variadic-min n-fixed))
(do
(put recur-entry-box 0 (fn [& recur-args] (apply self recur-args)))
(put arities n-fixed f)))))
(set self (fn [& fn-args]
(let [n (length fn-args)
f (get arities n)]
@ -1450,16 +1473,9 @@
rest-pat (param-info :rest)
defining-ns (ctx-current-ns ctx)]
(var self nil)
(set self (fn [& fn-args]
(var fn-bindings @{})
(table/setproto fn-bindings bindings)
(var i 0)
(each pat fixed-pats
(destructure-bind ctx fn-bindings pat (fn-args i))
(++ i))
(when rest-pat
(destructure-bind ctx fn-bindings rest-pat (tuple/slice fn-args i)))
(put fn-bindings :jolt/loop-fn self)
(var recur-entry nil)
(def run-body (fn [fn-bindings]
(put fn-bindings :jolt/loop-fn recur-entry)
(when fn-name (bind-put fn-bindings fn-name self))
# Use defining namespace for symbol resolution
(def saved-ns (ctx-current-ns ctx))
@ -1473,6 +1489,32 @@
(set result (eval-form ctx fn-bindings body-form)))
(ctx-set-current-ns ctx saved-ns)
result))
(set self (fn [& fn-args]
(var fn-bindings @{})
(table/setproto fn-bindings bindings)
(var i 0)
(each pat fixed-pats
(destructure-bind ctx fn-bindings pat (fn-args i))
(++ i))
(when rest-pat
(destructure-bind ctx fn-bindings rest-pat (tuple/slice fn-args i)))
(run-body fn-bindings)))
# recur re-enters here: for a variadic fn it takes n-fixed + 1
# args, the LAST bound DIRECTLY as the rest seq (Clojure) — going
# back through the varargs collector wrapped the seq in a fresh
# 1-element rest list, so it never emptied (the jolt-4df hang).
(set recur-entry
(if rest-pat
(fn [& recur-args]
(var fn-bindings @{})
(table/setproto fn-bindings bindings)
(var i 0)
(each pat fixed-pats
(destructure-bind ctx fn-bindings pat (recur-args i))
(++ i))
(destructure-bind ctx fn-bindings rest-pat (get recur-args i))
(run-body fn-bindings))
self))
self)))
"let*" (let [bind-vec (in form 1)
body (tuple/slice form 2)]

19
test/spec/functions-spec.janet
View file

@ -162,3 +162,22 @@
["char-name space" "\"space\"" "(char-name-string \\space)"]
["char-name newline" "\"newline\"" "(char-name-string \\newline)"]
["char-name none" "nil" "(char-name-string \\a)"])
# recur into a VARIADIC fn arity binds the LAST recur arg directly as the
# rest seq (Clojure: recur to a variadic head takes n-fixed + 1 args, no
# re-collection). The interpreter used to re-enter through the varargs
# collector, wrapping the seq in a fresh 1-element rest list — xs never
# emptied and the loop hung (jolt-4df).
(defspec "functions / recur into variadic arity"
["counts rest via recur" "3"
"((fn cnt [acc & xs] (if (seq xs) (recur (inc acc) (rest xs)) acc)) 0 :a :b :c)"]
["zero-fixed variadic" "4"
"((fn f [& xs] (if (< (count xs) 4) (recur (cons :x xs)) (count xs))) :a)"]
["rest empties to nil" "(quote (:done))"
"((fn f [& xs] (if xs (recur (next xs)) (list :done))) 1 2)"]
["multi-arity variadic recur" "6"
"((fn ma ([a] a) ([a & xs] (if (seq xs) (recur (+ a (first xs)) (rest xs)) a))) 1 2 3)"]
["recur passes nil rest" ":empty"
"((fn f [acc & xs] (if (seq xs) (recur acc (rest xs)) :empty)) 0 1)"]
["fixed-arity recur untouched" "10"
"((fn f [n acc] (if (pos? n) (recur (dec n) (+ acc 2)) acc)) 5 0)"])