parser: implement switch statement

A VM instruction `EqualSet` has been added to preserve the left
operand on the stack in case of failure, to allow efficient
multiple tests on the same value.
Both the pattern 'if/else if' and the classical case clauses have
been implemented.

1 files changed, 23 insertions, 12 deletions

diff --git a/parser/interpreter_test.go b/parser/interpreter_test.go
index 02cd105..d73d282 100644
--- a/parser/interpreter_test.go
+++ b/parser/interpreter_test.go
@@ -125,22 +125,33 @@ f(3)`, res: "4"},
 	})
 }
 
-/*
 func TestSwitch(t *testing.T) {
-	run(t, []etest{{
-		src: `
-func f(a int) int {
+	src0 := `func f(a int) int {
 	switch a {
-	default:
-		a = 0
-	case 1,2:
-		a = a+1
-	case 3:
-		a = a+2
+	default:  a = 0
+	case 1,2: a = a+1
+	case 3:   a = a+2
+	}
+	return a
+}
+`
+	src1 := `func f(a int) int {
+	switch {
+	case a < 3: return 2
+	case a < 5: return 5
+	default:  a = 0
 	}
 	return a
 }
-f(3)`, res: "5"},
+`
+	run(t, []etest{
+		{src: src0 + "f(1)", res: "2"},
+		{src: src0 + "f(2)", res: "3"},
+		{src: src0 + "f(3)", res: "5"},
+		{src: src0 + "f(4)", res: "0"},
+
+		{src: src1 + "f(1)", res: "2"},
+		{src: src1 + "f(4)", res: "5"},
+		{src: src1 + "f(6)", res: "0"},
 	})
 }
-*/