support initial state

lib.go

@@ -23,6 +23,7 @@ type Editor interface {
 type editorFunc[S any] struct {
 	edit         func(rune, S) ([]rune, S)
 	releaseState func(S) []rune
+	init         S
 }
 
 // Writer implements the io.Writer interface, passing the input to every editor in the configured sequence, and
@@ -34,6 +35,10 @@ type Writer struct {
 	err    error
 }
 
+func (e editorFunc[S]) initialize() any {
+	return e.init
+}
+
 func (e editorFunc[S]) Edit(r rune, state any) ([]rune, any) {
 	s, _ := state.(S)
 	return e.edit(r, s)
@@ -44,8 +49,9 @@ func (e editorFunc[S]) ReleaseState(state any) []rune {
 	return e.releaseState(s)
 }
 
-// Func can be used to define an Editor providing only the edit and releaseState functions.
-func Func[S any](edit func(r rune, state S) ([]rune, S), releaseState func(S) []rune) Editor {
+// FuncInit can be used to define an Editor providing only the edit and releaseState functions, and the initial
+// state.
+func FuncInit[S any](edit func(r rune, state S) ([]rune, S), releaseState func(S) []rune, init S) Editor {
 	if edit == nil {
 		edit = func(r rune, s S) ([]rune, S) { return []rune{r}, s }
 	}
@@ -54,7 +60,13 @@ func Func[S any](edit func(r rune, state S) ([]rune, S), releaseState func(S) []
 		releaseState = func(S) []rune { return nil }
 	}
 
-	return editorFunc[S]{edit: edit, releaseState: releaseState}
+	return editorFunc[S]{edit: edit, releaseState: releaseState, init: init}
+}
+
+// Func can be used to define an Editor providing only the edit and releaseState functions.
+func Func[S any](edit func(r rune, state S) ([]rune, S), releaseState func(S) []rune) Editor {
+	var s S
+	return FuncInit(edit, releaseState, s)
 }
 
 // Replace is a built-in editor for simple replace operations. The arguments are mapped such that the ones at
@@ -96,9 +108,11 @@ func SingleLine() Editor {
 // New initializes an editing writer. The editor instances will be called in the order they are passed in to
 // New.
 func New(out io.Writer, e ...Editor) *Writer {
+	seq := sequence(e...)
 	return &Writer{
 		out:    out,
-		editor: sequence(e...),
+		editor: seq,
+		state:  seq.(interface{ initialize() any }).initialize(),
 	}
 }
 

lib_test.go

@@ -181,3 +181,28 @@ func TestFlush(t *testing.T) {
 		}
 	})
 }
+
+func TestInit(t *testing.T) {
+	edit := func(r rune, lineStart bool) ([]rune, bool) {
+		if r == '\n' {
+			return []rune{'\n'}, true
+		}
+
+		if lineStart {
+			return append([]rune("> "), r), false
+		}
+
+		return []rune{r}, false
+	}
+
+	var b bytes.Buffer
+	e := textedit.FuncInit(edit, func(bool) []rune { return nil }, true)
+	w := textedit.New(&b, e)
+	if _, err := w.Write([]byte("quoted\nemail")); err != nil {
+		t.Fatal(err)
+	}
+
+	if b.String() != "> quoted\n> email" {
+		t.Fatal(b.String())
+	}
+}

sequence.go

@@ -57,8 +57,16 @@ func sequenceRelease(e []Editor) func([]any) []rune {
 }
 
 func sequence(e ...Editor) Editor {
-	return Func(
+	init := make([]any, len(e))
+	for i, ei := range e {
+		if initializer, ok := ei.(interface{ initialize() any }); ok {
+			init[i] = initializer.initialize()
+		}
+	}
+
+	return FuncInit(
 		sequenceEdit(e),
 		sequenceRelease(e),
+		init,
 	)
 }