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ocaml: phase 2 references ref/!/:= (+6 tests, 189 total)
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ref is a builtin boxing its arg in a one-element list. Prefix ! parses
to (:deref ...) and reads via (nth cell 0). := joins the binop
precedence table at level 1 right-assoc and mutates via set-nth!.
Closures share the underlying cell.
This commit is contained in:
giles
2026-05-08 08:07:26 +00:00
parent 9b833a9442
commit a11f3c33b6
4 changed files with 51 additions and 6 deletions
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24
lib/ocaml/eval.sx
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@@ -38,7 +38,10 @@
(list "min" (fn (a) (fn (b) (if (< a b) a b))))
(list "fst" (fn (p) (nth p 1)))
(list "snd" (fn (p) (nth p 2)))
(list "ignore" (fn (x) nil)))))
(list "ignore" (fn (x) nil))
;; References. A ref cell is a one-element list; ! reads it and
;; := mutates it via set-nth!.
(list "ref" (fn (x) (list x))))))
(define ocaml-env-lookup
(fn (env name)
@@ -235,11 +238,22 @@
(else (error (str "ocaml-eval: unbound variable " name))))))
((= tag "neg") (- 0 (ocaml-eval (nth ast 1) env)))
((= tag "not") (not (ocaml-eval (nth ast 1) env)))
((= tag "deref")
(let ((cell (ocaml-eval (nth ast 1) env)))
(nth cell 0)))
((= tag "op")
(ocaml-eval-op
(nth ast 1)
(ocaml-eval (nth ast 2) env)
(ocaml-eval (nth ast 3) env)))
(let ((op (nth ast 1)))
(cond
;; := mutates the lhs cell — short-circuit before generic
;; eval-op so we still evaluate lhs (to obtain the cell).
((= op ":=")
(let ((cell (ocaml-eval (nth ast 2) env))
(new-val (ocaml-eval (nth ast 3) env)))
(begin (set-nth! cell 0 new-val) nil)))
(else
(ocaml-eval-op op
(ocaml-eval (nth ast 2) env)
(ocaml-eval (nth ast 3) env))))))
((= tag "if")
(if (ocaml-eval (nth ast 1) env)
(ocaml-eval (nth ast 2) env)