add skeleton for instruction constructors

internal/inst/table_test.go

@@ -40,6 +40,9 @@ func TestInstructionProperties(t *testing.T) {
 		if len(i.Forms) == 0 {
 			t.Errorf("instruction %s has no forms", i.Opcode)
 		}
+		if len(i.Arities()) == 0 {
+			t.Errorf("instruction %s has empty arities list", i.Opcode)
+		}
 	}
 }
 

internal/inst/types.go

@@ -28,6 +28,14 @@ type Form struct {
 	ImplicitOperands []ImplicitOperand
 }
 
+func (f Form) Signature() []string {
+	s := make([]string, len(f.Operands))
+	for i, op := range f.Operands {
+		s[i] = op.Type
+	}
+	return s
+}
+
 type Operand struct {
 	Type   string
 	Action Action