haskell: Phase 9 — hk-run-io catches errors and appends to io-lines

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

lib/haskell/eval.sx

@@ -1163,7 +1163,14 @@
 
 (define
   hk-run-io
-  (fn (src) (do (set! hk-io-lines (list)) (hk-run src) hk-io-lines)))
+  (fn
+    (src)
+    (do
+      (set! hk-io-lines (list))
+      (guard
+        (e (true (append! hk-io-lines (if (string? e) e (str e)))))
+        (hk-deep-force (hk-run src)))
+      hk-io-lines)))
 
 (define hk-stdin-lines (list))
 
@@ -1176,7 +1183,9 @@
     (begin
       (set! hk-io-lines (list))
       (set! hk-stdin-lines stdin-lines)
-      (hk-run src)
+      (guard
+        (e (true (append! hk-io-lines (if (string? e) e (str e)))))
+        (hk-deep-force (hk-run src)))
       hk-io-lines)))
 
 (define hk-env0 (hk-init-env))

lib/haskell/tests/io-input.sx

@@ -64,12 +64,11 @@
 
 (hk-test
   "readFile error on missing file"
-  (guard
-    (e (true (>= (index-of e "file not found") 0)))
-    (begin
-      (set! hk-vfs (dict))
-      (hk-run-io "main = readFile \"no.txt\" >>= putStrLn")
-      false))
+  (begin
+    (set! hk-vfs (dict))
+    (let
+      ((lines (hk-run-io "main = readFile \"no.txt\" >>= putStrLn")))
+      (>= (index-of (str lines) "file not found") 0)))
   true)
 
 (hk-test

plans/haskell-completeness.md

@@ -131,7 +131,7 @@ No OCaml changes are needed. The view type is fully representable as an SX dict.
 - [x] Partial functions emit proper error messages: `head []` →
   `"Prelude.head: empty list"`, `tail []` → `"Prelude.tail: empty list"`,
   `fromJust Nothing` → `"Maybe.fromJust: Nothing"`.
-- [ ] Top-level `hk-run-io` catches `hk-error` tag and returns it as a tagged
+- [x] Top-level `hk-run-io` catches `hk-error` tag and returns it as a tagged
   error result so test suites can inspect it without crashing.
 - [ ] `hk-test-error` helper in `testlib.sx`:
   `(hk-test-error "desc" thunk expected-substring)` — asserts the thunk raises
@@ -293,6 +293,19 @@ No OCaml changes are needed. The view type is fully representable as an SX dict.
 
 _Newest first._
 
+**2026-05-07** — Phase 9 `hk-run-io` catches errors, appends to io-lines:
+- Wrapped both `hk-run-io` and `hk-run-io-with-input` in `(guard (e (true …)))`
+  that appends the caught exception to `hk-io-lines`. Also added `hk-deep-force`
+  inside the guard so `main`'s thunk actually evaluates (post-lazy-CAFs change
+  it was a thunk, was previously not forced — IO actions never fired in
+  programs that returned the thunk to `hk-run-io`). Test suites now see error
+  output as the last line of `hk-io-lines` instead of crashing.
+- Updated one io-input test that used an outer `guard` to look for
+  `"file not found"` in the io-lines string instead.
+- Verified across program-io (10/10), io-input (11/11), program-fizzbuzz
+  (12/12), program-calculator (5/5), program-roman (14/14), program-wordcount
+  (10/10), program-showadt (5/5), program-showio (5/5), eval.sx (64/64).
+
 **2026-05-07** — Phase 9 partial functions emit proper error messages:
 - Added empty-list catch clauses to `head`, `tail` in the prelude. Added
   `fromJust`, `fromMaybe`, `isJust`, `isNothing` (the last three were missing).