Example extended.

examples_test.go

@@ -7,7 +7,7 @@ import (
 	"git.makaay.nl/mauricem/go-parsekit"
 )
 
-func Example_minimal() {
+func Example_minimalAnnotated() {
 	// Let's write a small example for parsing a really basic calculator.
 	// The calculator understands input that looks like:
 	//
@@ -65,15 +65,15 @@ func Example_minimal() {
 	}
 
 	// All is ready for our parser. We now can create a new Parser struct.
-	// We need to tell it what the start state is. In our case, it's the
+	// We need to tell it what the start state is. In our case, it is
-	// of course the number state.
+	// the number state, since the calculation must start with a number.
 	parser := parsekit.NewParser(numberHandler)
 
-	// Let's fee the parser some input to work with.
+	// Let's feed the parser some input to work with.
 	run := parser.Parse("153+ 22+31 - 4- 6+42")
 
-	// We can step through the results of the parsing process by repeated
+	// We can now step through the results of the parsing process by repeated
-	// calls to run.Next(). Next() returns the next parse item, a parse
+	// calls to run.Next(). Next() returns either the next parse item, a parse
 	// error or an end of file. Let's dump the parse results and handle the
 	// computation while we're at it.
 	sum := 0
@@ -118,6 +118,68 @@ func Example_minimal() {
 	// Outcome of computation: 238
 }
 
+func Example_minimal() {
+	var c, a, m = parsekit.C, parsekit.A, parsekit.M
+
+	var number = c.OneOrMore(a.Digit)
+	var whitespace = m.Drop(c.Opt(a.Whitespace))
+	var operator = c.Seq(whitespace, c.Any(a.Plus, a.Minus), whitespace)
+
+	const (
+		numberType parsekit.ItemType = iota
+		operatorType
+	)
+
+	var operatorHandler parsekit.StateHandler
+
+	numberHandler := func(p *parsekit.P) {
+		p.Expects("a number")
+		if p.On(number).Accept().End() {
+			p.EmitLiteral(numberType)
+			p.RouteTo(operatorHandler)
+		}
+	}
+
+	operatorHandler = func(p *parsekit.P) {
+		if p.On(operator).Accept().End() {
+			p.EmitLiteral(operatorType)
+			p.RouteTo(numberHandler)
+		} else {
+			p.ExpectEndOfFile()
+		}
+	}
+
+	parser := parsekit.NewParser(numberHandler)
+	run := parser.Parse("153+ 22+31 - 4- 6+42")
+
+	sum := 0
+	op := +1
+	for {
+		item, err, ok := run.Next()
+		switch {
+		case !ok && err == nil:
+			fmt.Println("Outcome of computation:", sum)
+			return
+		case !ok:
+			fmt.Printf("Error: %s\n", err)
+			return
+		default:
+			switch {
+			case item.Type == operatorType && item.Value == "+":
+				op = +1
+			case item.Type == operatorType && item.Value == "-":
+				op = -1
+			default:
+				nr, _ := strconv.Atoi(item.Value)
+				sum += op * nr
+			}
+		}
+	}
+
+	// Output:
+	// Outcome of computation: 238
+}
+
 func ExampleItemType() {
 	// Make use of positive values. Ideally, define your ItemTypes using
 	// iota for easy automatic value management like this: