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Merge loops/sx-vm-extensions into architecture: rational cleanup

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(/ int int) returns float per spec/host parity (was leaking exact rationals
into arithmetic + CSS, e.g. tw-opacity 1/20); rational operand still yields
exact rational. number?/exact? recognise Rational. test-rationals typo fix.
OCaml conformance 4834->4863, rational/numeric-tower/arithmetic/tw-opacity green.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
This commit is contained in:
giles
2026-06-29 07:03:30 +00:00
parent d122aed0cb e90c8fdd97
commit 1597eaa4f8
3 changed files with 15 additions and 7 deletions
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12
hosts/ocaml/lib/sx_primitives.ml
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@@ -218,7 +218,14 @@ let () =
Number (List.fold_left (fun acc a -> acc *. as_number a) 1.0 args));
register "/" (fun args ->
match args with
| [Integer a; Integer b] -> make_rat a b
(* (/ int int): exact when divisible → integer, else inexact float.
Matches spec ("inexact float") + JS host (backward-compatible) +
test-numeric-tower ((/ 6 2)=3, (/ 1 4)=0.25, (/ 5 2)=2.5). Exact
rationals come ONLY from literals / make-rational, so a rational
OPERAND keeps the result exact (cases below) — but two integers do
NOT silently produce a rational (that diverged from the JS host). *)
| [Integer a; Integer b] when b <> 0 && a mod b = 0 -> Integer (a / b)
| [Integer a; Integer b] -> Number (float_of_int a /. float_of_int b)
| [Rational(an,ad); Integer b] -> make_rat an (ad * b)
| [Integer a; Rational(bn,bd)] -> make_rat (a * bd) bn
| [Rational(an,ad); Rational(bn,bd)] -> rat_div (an, ad) (bn, bd)
@@ -397,6 +404,7 @@ let () =
register "exact?" (fun args ->
match args with
| [Integer _] -> Bool true
| [Rational _] -> Bool true (* rationals are exact *)
| [Number _] -> Bool false
| [_] -> Bool false
| _ -> raise (Eval_error "exact?: 1 arg"));
@@ -833,7 +841,7 @@ let () =
match args with [a] -> Bool (is_nil a) | _ -> raise (Eval_error "nil?: 1 arg"));
register "number?" (fun args ->
match args with
| [Integer _] | [Number _] -> Bool true
| [Integer _] | [Number _] | [Rational _] -> Bool true
| [_] -> Bool false
| _ -> raise (Eval_error "number?: 1 arg"));
register "integer?" (fun args ->

8
hosts/ocaml/lib/sx_vm.ml
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@@ -829,10 +829,10 @@ and run vm =
let b = pop vm and a = pop vm in
push vm (match a, b with
| Integer x, Integer y when y <> 0 && x mod y = 0 -> Integer (x / y)
(* Non-divisible Integer/Integer must delegate to the "/" primitive:
it returns an exact Rational (e.g. 1/2), matching CEK semantics.
Inlining float division here (0.5) diverges from the interpreter
and breaks numeric equality against rational results. *)
(* Non-divisible Integer/Integer + any Rational operand delegate to
the "/" primitive (single source of truth): (/ 5 2)=2.5 float,
(/ 1/2 2)=1/4 rational. Keeping the VM in lockstep with the
primitive avoids diverging from the CEK interpreter. *)
| Number x, Number y -> Number (x /. y)
| Integer x, Number y -> Number (float_of_int x /. y)
| Number x, Integer y -> Number (x /. float_of_int y)

2
spec/tests/test-rationals.sx
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@@ -101,7 +101,7 @@
"rationals:float-contagion"
(deftest "rational + float = float" (assert (float? (+ 1/3 0.5))))
(deftest "float + rational = float" (assert (float? (+ 0.5 1/3))))
(deftest "rational * float = float" (assert (float? (* 1/2 2))))
(deftest "rational * float = float" (assert (float? (* 1/2 2.0))))
(deftest "rational - float = float" (assert (float? (- 1/2 0.1)))))
;; --------------------------------------------------------------------------