1 files changed, 81 insertions, 0 deletions
diff --git a/pointer.go b/pointer.go
new file mode 100644
index 0000000..92b2bcb
--- /dev/null
+++ b/pointer.go
@@ -0,0 +1,81 @@
+package parsec
+
+import (
+	"strings"
+	"unicode/utf8"
+)
+
+const (
+	EOF rune = -1
+)
+
+func Input(s string) Pointer {
+	return Pointer{s, 0}
+}
+
+type Pointer struct {
+	input string
+	pos   int
+}
+
+func (p Pointer) Advance(i int) Pointer {
+	return Pointer{p.input, p.pos + i}
+}
+
+func (p Pointer) Get() string {
+	return p.input[p.pos:]
+}
+
+func (p Pointer) Remaining() int {
+	remaining := len(p.input) - p.pos
+	if remaining < 0 {
+		return 0
+	}
+	return remaining
+}
+
+func (p Pointer) Next() (rune, Pointer) {
+	if int(p.pos) >= len(p.input) {
+		return EOF, p
+	}
+	r, w := utf8.DecodeRuneInString(p.input[p.pos:])
+	return r, p.Advance(w)
+}
+
+func (p Pointer) HasPrefix(s string) bool {
+	return strings.HasPrefix(p.input[p.pos:], s)
+}
+
+func (p Pointer) Accept(valid string) (string, Pointer) {
+	c, newP := p.Next()
+	if strings.ContainsRune(valid, c) {
+		return string(c), newP
+	}
+	return "", p
+}
+
+func (p Pointer) AcceptRun(valid string) (string, Pointer) {
+	matched := 0
+	for p.pos+matched < len(p.input) {
+		r, w := utf8.DecodeRuneInString(p.input[p.pos+matched:])
+		if !strings.ContainsRune(valid, r) {
+			break
+		}
+		matched += w
+	}
+
+	return p.input[p.pos : p.pos+matched], p.Advance(matched)
+}
+
+func (p Pointer) AcceptUntil(invalid string) (string, Pointer) {
+	matched := 0
+	for p.pos+matched < len(p.input) {
+		r, w := utf8.DecodeRuneInString(p.input[p.pos+matched:])
+		if strings.ContainsRune(invalid, r) {
+			break
+		}
+		matched += w
+	}
+
+	return p.input[p.pos : p.pos+matched], p.Advance(matched)
+}