Switch to add/remove instruction mutation

grow/mutate.go

@@ -0,0 +1,36 @@
+package grow
+
+import "math"
+import "math/rand"
+
+import "github.com/firestuff/subcoding/gen"
+import "github.com/firestuff/subcoding/vm"
+
+func Mutate(prog *vm.Program) {
+	target := int(math.Max(2, rand.NormFloat64()*10+15))
+
+	if len(prog.Functions[0].Instructions) < target {
+		addInstruction(prog, prog.Functions[0])
+	} else {
+		removeInstruction(prog, prog.Functions[0])
+	}
+}
+
+func addInstruction(prog *vm.Program, fnc *vm.Function) {
+	if len(fnc.Instructions) == 0 {
+		fnc.Instructions = append(fnc.Instructions, gen.RandInstruction(prog))
+	} else {
+		i := rand.Intn(len(fnc.Instructions))
+		fnc.Instructions = append(fnc.Instructions[:i+1], fnc.Instructions[i:]...)
+		fnc.Instructions[i] = gen.RandInstruction(prog)
+	}
+}
+
+func removeInstruction(prog *vm.Program, fnc *vm.Function) {
+	if len(fnc.Instructions) == 0 {
+		return
+	}
+
+	i := rand.Intn(len(fnc.Instructions))
+	fnc.Instructions = append(fnc.Instructions[:i], fnc.Instructions[i+1:]...)
+}