feat(operators): support global binary operator overloads

Resolve exact operand types and preserve declared operator return types.
Reject implicit STRING to BOOLEAN conversion at typed expression boundaries.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

7 files changed, 90 insertions, 0 deletions

diff --git a/tests/i/operator-global/case.json b/tests/i/operator-global/case.json
new file mode 100644
index 0000000..0967ef4
--- /dev/null
+++ b/tests/i/operator-global/case.json
@@ -0,0 +1 @@
+{}
diff --git a/tests/i/operator-global/expected.txt b/tests/i/operator-global/expected.txt
new file mode 100644
index 0000000..3460ce8
--- /dev/null
+++ b/tests/i/operator-global/expected.txt
@@ -0,0 +1,5 @@
+7
+2!
+comparison
+6
+5xyTRUE
diff --git a/tests/i/operator-global/notes.md b/tests/i/operator-global/notes.md
new file mode 100644
index 0000000..1026071
--- /dev/null
+++ b/tests/i/operator-global/notes.md
@@ -0,0 +1,7 @@
+# operator-global
+
+Human review: pending. Expected output was independently traced by AI, not captured from cpsc.
+
+Basis: operator overloading is a project extension, with exact parameter types.
+
+Trace: Box additions sum 2 + 3 + 2 to 7. Concatenation returns 2!. The comparison deliberately returns STRING, printed as comparison. Reversed INTEGER + Box gives 4 + 2 = 6. Builtin operations still print 5xyTRUE.
diff --git a/tests/i/operator-global/program.cps b/tests/i/operator-global/program.cps
new file mode 100644
index 0000000..9d27fcb
--- /dev/null
+++ b/tests/i/operator-global/program.cps
@@ -0,0 +1,28 @@
+TYPE Box
+DECLARE Value : INTEGER
+ENDTYPE
+OVERLOAD FUNCTION OPERATOR+(a : Box, b : Box) RETURNS Box
+DECLARE result : Box
+result.Value <- a.Value + b.Value
+RETURN result
+ENDFUNCTION
+OVERLOAD FUNCTION OPERATOR&(a : Box, b : STRING) RETURNS STRING
+RETURN NUM_TO_STR(a.Value) & b
+ENDFUNCTION
+OVERLOAD FUNCTION OPERATOR<(a : Box, b : Box) RETURNS STRING
+RETURN "comparison"
+ENDFUNCTION
+OVERLOAD FUNCTION OPERATOR+(a : INTEGER, b : Box) RETURNS INTEGER
+RETURN a + b.Value
+ENDFUNCTION
+DECLARE a : Box
+DECLARE b : Box
+DECLARE result : Box
+a.Value <- 2
+b.Value <- 3
+result <- a + b + a
+OUTPUT result.Value
+OUTPUT a & "!"
+OUTPUT a < b
+OUTPUT 4 + a
+OUTPUT 2 + 3, "x" & "y", 1 < 2
diff --git a/tests/iii/operator-global-errors/case.json b/tests/iii/operator-global-errors/case.json
new file mode 100644
index 0000000..eeb9965
--- /dev/null
+++ b/tests/iii/operator-global-errors/case.json
@@ -0,0 +1,24 @@
+{
+  "errors": [
+    {
+      "reason": "Cannot implicitly convert STRING to BOOLEAN",
+      "line": 12
+    },
+    {
+      "reason": "Operator \\+ cannot be applied to a record",
+      "line": 13
+    },
+    {
+      "reason": "requires a record, class or enum operand",
+      "line": 14
+    },
+    {
+      "reason": "Invalid operand count",
+      "line": 17
+    },
+    {
+      "reason": "cannot be redefined",
+      "line": 20
+    }
+  ]
+}
diff --git a/tests/iii/operator-global-errors/notes.md b/tests/iii/operator-global-errors/notes.md
new file mode 100644
index 0000000..24bb113
--- /dev/null
+++ b/tests/iii/operator-global-errors/notes.md
@@ -0,0 +1,3 @@
+# operator-global-errors
+
+Reject a STRING comparison result assigned to BOOLEAN, implicit INTEGER-to-REAL overload matching, builtin-only overloads, wrong arity and return-type-only duplicates.
diff --git a/tests/iii/operator-global-errors/program.cps b/tests/iii/operator-global-errors/program.cps
new file mode 100644
index 0000000..23bfae1
--- /dev/null
+++ b/tests/iii/operator-global-errors/program.cps
@@ -0,0 +1,22 @@
+TYPE Box
+DECLARE Value : INTEGER
+ENDTYPE
+OVERLOAD FUNCTION OPERATOR+(a : Box, b : REAL) RETURNS INTEGER
+RETURN 1
+ENDFUNCTION
+OVERLOAD FUNCTION OPERATOR<(a : Box, b : Box) RETURNS STRING
+RETURN "text"
+ENDFUNCTION
+DECLARE a : Box
+DECLARE flag : BOOLEAN
+flag <- a < a
+OUTPUT a + 1
+OVERLOAD FUNCTION OPERATOR&(a : INTEGER, b : STRING) RETURNS STRING
+RETURN b
+ENDFUNCTION
+OVERLOAD FUNCTION OPERATOR*(a : Box) RETURNS INTEGER
+RETURN 1
+ENDFUNCTION
+OVERLOAD FUNCTION OPERATOR+(a : Box, b : REAL) RETURNS REAL
+RETURN 2.0
+ENDFUNCTION