Added crude loop protection to the parser, which should prevent parsers running in circles (happened to me a few times too).

example_dutchpostcode_test.go

@@ -1,6 +1,7 @@
 // In this example, a Parser is created that can parse and normalize Dutch postcodes
 // The implementation uses only TokenHandler functions and does not implement a
 // full-fledged state-based Parser for it.
+
 package parsekit_test
 
 import (

examples_state_test.go

@@ -15,20 +15,22 @@ import (
 
 type letterCollection []string
 
-func (l *letterCollection) parseStart(p *parsekit.ParseAPI) {
-	for p.On(parsekit.C.MinMax(1, 3, parsekit.A.AnyRune)).Accept() {
-		*l = append(*l, p.BufLiteral())
-		p.BufClear()
-	}
-	p.ExpectEndOfFile()
+func (l *letterCollection) AddChopped(s string, chunkSize int) *parsekit.Error {
+	parser := parsekit.NewParser(func(p *parsekit.ParseAPI) {
+		for p.On(parsekit.C.MinMax(1, chunkSize, parsekit.A.AnyRune)).Accept() {
+			*l = append(*l, p.BufLiteral())
+			p.BufClear()
+		}
+	})
+	return parser.Execute(s)
 }
 
 func Example_usingSliceAsParserState() {
 	letters := &letterCollection{}
-	parser := parsekit.NewParser(letters.parseStart)
-	err := parser.Execute("¡Any will dö!")
+	letters.AddChopped("This string will", 4)
+	letters.AddChopped("be cut to bits!!!!!!", 8)
 
-	fmt.Printf("Matches = %q, Error = %s\n", *letters, err)
+	fmt.Printf("Matches = %q", *letters)
 	// Output:
-	// Matches = ["¡An" "y w" "ill" " dö" "!"], Error = <nil>
+	// Matches = ["This" " str" "ing " "will" "be cut t" "o bits!!" "!!!!"]
 }

parsehandler.go

@@ -18,16 +18,17 @@ type ParseHandler func(*ParseAPI)
 // ParseAPI holds the internal state of a parse run and provides an API to
 // ParseHandler methods to communicate with the parser.
 type ParseAPI struct {
-	input        string       // the input that is being scanned by the parser
-	inputPos     int          // current byte cursor position in the input
-	cursorLine   int          // current rune cursor row number in the input
-	cursorColumn int          // current rune cursor column position in the input
-	len          int          // the total length of the input in bytes
-	newline      bool         // keep track of when we have scanned a newline
-	expecting    string       // a description of what the current state expects to find (see P.Expects())
-	buffer       stringBuffer // an efficient buffer, used to build string values (see P.Accept())
-	err          *Error       // error during parsing, retrieved by Error(), further ParseAPI calls are ignored
-	stopped      bool         // a boolean set to true by Stop(), further ParseAPI calls are ignored
+	input        string          // the input that is being scanned by the parser
+	inputPos     int             // current byte cursor position in the input
+	loopCheck    map[string]bool // used for parser loop detection
+	cursorLine   int             // current rune cursor row number in the input
+	cursorColumn int             // current rune cursor column position in the input
+	len          int             // the total length of the input in bytes
+	newline      bool            // keep track of when we have scanned a newline
+	expecting    string          // a description of what the current state expects to find (see P.Expects())
+	buffer       stringBuffer    // an efficient buffer, used to build string values (see P.Accept())
+	err          *Error          // error during parsing, retrieved by Error(), further ParseAPI calls are ignored
+	stopped      bool            // a boolean set to true by Stop(), further ParseAPI calls are ignored
 
 	LastMatch string // a string representation of the last matched input data
 }
@@ -62,6 +63,16 @@ func (p *ParseAPI) isStoppedOrInError() bool {
 	return p.stopped || p.err != nil
 }
 
+func (p *ParseAPI) checkForLoops() {
+	pc, file, line, _ := runtime.Caller(2)
+	id := fmt.Sprintf("%s:%d", file, line)
+	if _, ok := p.loopCheck[id]; ok {
+		caller := runtime.FuncForPC(pc)
+		panic(fmt.Sprintf("Loop detected in parser in %s at %s, line %d", caller.Name(), file, line))
+	}
+	p.loopCheck[id] = true
+}
+
 // peek returns but does not advance the cursor to the next rune in the input.
 // Returns the rune, its width in bytes and a boolean.
 //

parsehandler_on.go

@@ -38,6 +38,7 @@ package parsekit
 //     }
 func (p *ParseAPI) On(tokenHandler TokenHandler) *ParseAPIOnAction {
 	p.panicWhenStoppedOrInError()
+	p.checkForLoops()
 
 	// Perform the matching operation.
 	m := &TokenAPI{p: p}
@@ -109,6 +110,10 @@ func (a *ParseAPIOnAction) Stay() bool {
 // While doing so, it keeps tracks of newlines that are encountered, so we
 // can report on line + column positions on error.
 func (a *ParseAPIOnAction) advanceCursor() {
+	if a.p.inputPos == a.inputPos {
+		return
+	}
+	a.p.loopCheck = map[string]bool{}
 	a.p.inputPos = a.inputPos
 	for _, r := range a.input {
 		if a.p.newline {

parsehandler_test.go

@@ -73,3 +73,36 @@ func TestGivenInputInvalidForStringInterpretation_BufInterpreted_SetsError(t *te
 		t.Fatalf("Got unexpected error: %s", err.Error())
 	}
 }
+
+type parserWithLoop struct {
+	loopCounter int
+}
+
+func (l *parserWithLoop) first(p *parsekit.ParseAPI) {
+	p.On(parsekit.A.ASCII).Accept()
+	p.Handle(l.second)
+}
+
+func (l *parserWithLoop) second(p *parsekit.ParseAPI) {
+	p.On(parsekit.A.ASCII).Accept()
+	p.Handle(l.third)
+}
+
+func (l *parserWithLoop) third(p *parsekit.ParseAPI) {
+	if l.loopCounter++; l.loopCounter > 100 {
+		p.Error("Loop not detected by parsekit")
+		return
+	}
+	p.On(parsekit.A.ASCII).Accept()
+	p.Handle(l.first)
+}
+
+func TestGivenLoopingParserDefinition_ParserPanics(t *testing.T) {
+	looper := &parserWithLoop{}
+	parser := parsekit.NewParser(looper.first)
+	RunPanicTest(t, PanicTest{
+		func() { parser.Execute("Het houdt niet op, niet vanzelf") },
+		"Loop detected in parser in git.makaay.nl/mauricem/go-parsekit_test." +
+			"(*parserWithLoop).second at /home/ubuntu/Projects/Parsekit/go-parsekit" +
+			"/parsehandler_test.go, line 87"})
+}

parsekit.go

@@ -26,6 +26,7 @@ func (p *Parser) Execute(input string) *Error {
 		len:          len(input),
 		cursorLine:   1,
 		cursorColumn: 1,
+		loopCheck:    map[string]bool{},
 	}
 	api.Handle(p.startHandler)
 	if !api.stopped && api.err == nil {

tokenhandlers_builtin_test.go

@@ -46,6 +46,9 @@ func TestCombinators(t *testing.T) {
 		{"bbbbbX", c.Max(6, c.Rune('b')), true, "bbbbb"},
 		{"", c.MinMax(0, 0, c.Rune('c')), true, ""},
 		{"X", c.MinMax(0, 0, c.Rune('c')), true, ""},
+		{"cccc", c.MinMax(0, 5, c.Rune('c')), true, "cccc"},
+		{"ccccc", c.MinMax(0, 5, c.Rune('c')), true, "ccccc"},
+		{"cccccc", c.MinMax(0, 5, c.Rune('c')), true, "ccccc"},
 		{"cccccX", c.MinMax(0, 0, c.Rune('c')), true, ""},
 		{"cccccX", c.MinMax(0, 1, c.Rune('c')), true, "c"},
 		{"cccccX", c.MinMax(0, 5, c.Rune('c')), true, "ccccc"},