Fix guarded SKIP in ALT to respect guard expression

codegen/codegen.go

@@ -1902,9 +1902,21 @@ func (g *Generator) generateAltBlock(alt *ast.AltBlock) {
 			g.write(fmt.Sprintf("case %s = <-%s:\n", goIdent(c.Variable), goIdent(c.Channel)))
 		}
 		g.indent++
+		guardedSkip := c.IsSkip && c.Guard != nil
+		if guardedSkip {
+			g.builder.WriteString(strings.Repeat("\t", g.indent))
+			g.write("if ")
+			g.generateExpression(c.Guard)
+			g.write(" {\n")
+			g.indent++
+		}
 		for _, s := range c.Body {
 			g.generateStatement(s)
 		}
+		if guardedSkip {
+			g.indent--
+			g.writeLine("}")
+		}
 		g.indent--
 	}
 	g.writeLine("}")

codegen/e2e_misc_test.go

@@ -233,6 +233,59 @@ func TestE2E_AltGuardedSkip(t *testing.T) {
 	}
 }
 
+func TestE2E_AltGuardedSkipTrue(t *testing.T) {
+	// Issue #77: ALT with channel case and guarded SKIP where guard is TRUE
+	// The SKIP fires immediately, then the channel send proceeds
+	occam := `SEQ
+  CHAN OF INT c:
+  INT result:
+  BOOL ready:
+  ready := TRUE
+  result := 0
+  PAR
+    SEQ
+      ALT
+        ready & SKIP
+          result := 99
+        c ? result
+          SKIP
+      c ! 42
+    c ? result
+  print.int(result)
+`
+	output := transpileCompileRun(t, occam)
+	expected := "42\n"
+	if output != expected {
+		t.Errorf("expected %q, got %q", expected, output)
+	}
+}
+
+func TestE2E_AltGuardedSkipFalse(t *testing.T) {
+	// Issue #77: ALT with channel case and guarded SKIP where guard is FALSE
+	// The SKIP guard is false, so the channel case fires
+	occam := `SEQ
+  CHAN OF INT c:
+  INT result:
+  BOOL ready:
+  ready := FALSE
+  result := 0
+  PAR
+    SEQ
+      ALT
+        ready & SKIP
+          result := 99
+        c ? result
+          SKIP
+    c ! 77
+  print.int(result)
+`
+	output := transpileCompileRun(t, occam)
+	expected := "77\n"
+	if output != expected {
+		t.Errorf("expected %q, got %q", expected, output)
+	}
+}
+
 func TestE2E_MultiLineAbbreviation(t *testing.T) {
 	// Issue #79: IS at end of line as continuation
 	occam := `SEQ

parser/parser_test.go

@@ -349,6 +349,38 @@ func TestAltBlockWithGuard(t *testing.T) {
 	}
 }
 
+func TestAltBlockWithGuardedSkip(t *testing.T) {
+	input := `ALT
+  ready & SKIP
+    some.proc()
+`
+	l := lexer.New(input)
+	p := New(l)
+	program := p.ParseProgram()
+	checkParserErrors(t, p)
+
+	if len(program.Statements) != 1 {
+		t.Fatalf("expected 1 statement, got %d", len(program.Statements))
+	}
+
+	alt, ok := program.Statements[0].(*ast.AltBlock)
+	if !ok {
+		t.Fatalf("expected AltBlock, got %T", program.Statements[0])
+	}
+
+	if len(alt.Cases) != 1 {
+		t.Fatalf("expected 1 case, got %d", len(alt.Cases))
+	}
+
+	c := alt.Cases[0]
+	if !c.IsSkip {
+		t.Error("expected IsSkip to be true")
+	}
+	if c.Guard == nil {
+		t.Error("expected guard expression, got nil")
+	}
+}
+
 func TestWhileLoop(t *testing.T) {
 	input := `WHILE x > 0
   x := x - 1