Added Validate method to Tq API struct

Author: mdm-code

example_test.go

@@ -36,3 +36,20 @@ role = "backend"
 	// Output:
 	// '10.0.0.2'
 }
+
+// ExampleTq_Validate shows how to use the Tq struct to validate whether a
+// given query is syntactically correct. The example shows how the error is
+// reported and represented as a string.
+func ExampleTq_Validate() {
+	query := "['servers'][['ip']"
+	config := toml.GoTOMLConf{}
+	goToml := toml.NewGoTOML(config)
+	adapter := toml.NewAdapter(goToml)
+	tq := tq.New(adapter)
+	err := tq.Validate(query)
+	fmt.Println(err)
+	// Output:
+	// ['servers'][['ip']
+	//             ^
+	// Parser error: expected ']' to terminate selector but got '['
+}

tq.go

@@ -32,6 +32,28 @@ func New(adapter toml.Adapter) *Tq {
 	}
 }
 
+// Validate checks if the query string is syntactically correct.
+func (t *Tq) Validate(query string) error {
+	reader := strings.NewReader(query)
+	scanner, err := scanner.New(reader)
+	if err != nil {
+		return err
+	}
+	lexer, err := lexer.New(scanner)
+	if err != nil {
+		return err
+	}
+	parser, err := parser.New(lexer)
+	if err != nil {
+		return err
+	}
+	_, err = parser.Parse()
+	if err != nil {
+		return err
+	}
+	return nil
+}
+
 // Run executes the query string against the input data and writes the output
 // data to the output writer.
 func (t *Tq) Run(input io.Reader, output io.Writer, query string) error {