Improve coverage for expressions, specifically Print

datalog/expressions.go

@@ -95,9 +95,6 @@ func (e *Expression) Print(symbols *SymbolTable) string {
 				return "<invalid expression: unary operation failed to pop value>"
 			}
 			res := op.(UnaryOp).Print(v)
-			if err != nil {
-				return "<invalid expression: binary operation failed to pop right value>"
-			}
 			s.Push(res)
 		case OpTypeBinary:
 			right, err := s.Pop()
@@ -160,6 +157,8 @@ func (op UnaryOp) Print(value string) string {
 		out = fmt.Sprintf("!%s", value)
 	case UnaryParens:
 		out = fmt.Sprintf("(%s)", value)
+	case UnaryLength:
+		out = fmt.Sprintf("%s.length()", value)
 	default:
 		out = fmt.Sprintf("unknown(%s)", value)
 	}
@@ -228,7 +227,7 @@ func (Length) Eval(value Term, symbols *SymbolTable) (Term, error) {
 	case TermTypeSet:
 		out = Integer(len(value.(Set)))
 	default:
-		return nil, fmt.Errorf("datalog: unexpected Negate value type: %d", value.Type())
+		return nil, fmt.Errorf("datalog: unexpected Length value type: %d", value.Type())
 	}
 	return out, nil
 }

datalog/expressions_test.go

@@ -1188,3 +1188,52 @@ func TestBinaryOr(t *testing.T) {
 		})
 	}
 }
+
+func TestPrint(t *testing.T) {
+	syms := SymbolTable{}
+	syms.Insert("abc")
+	testCases := []struct {
+		desc string
+		expr Expression
+		res  string
+	}{
+		{
+			desc: "number",
+			expr: Expression{Value{Integer(9)}},
+			res:  "9",
+		},
+		{
+			desc: "string",
+			expr: Expression{Value{syms.Sym("abc")}},
+			res:  "\"abc\"",
+		},
+		{
+			desc: "unary",
+			expr: Expression{Value{syms.Sym("abc")}, UnaryOp{Length{}}},
+			res:  "\"abc\".length()",
+		},
+		{
+			desc: "binary",
+			expr: Expression{Value{Integer(9)}, Value{Integer(4)}, BinaryOp{Mul{}}},
+			res:  "9 * 4",
+		},
+		{
+			desc: "parens",
+			expr: Expression{
+				Value{Integer(9)},
+				Value{Integer(3)},
+				BinaryOp{Add{}},
+				UnaryOp{Parens{}},
+				Value{Integer(4)},
+				BinaryOp{Div{}},
+			},
+			res: "(9 + 3) / 4",
+		},
+	}
+	for _, tc := range testCases {
+		t.Run(tc.desc, func(t *testing.T) {
+			p := tc.expr.Print(&syms)
+			require.Equal(t, tc.res, p)
+		})
+	}
+}