fixed column indexing

position.go

@@ -10,7 +10,7 @@ func (p *Position) Advance(rn rune) {
 	p.Index++
 	if rn == '\n' {
 		p.Line++
-		p.Column = 0
+		p.Column = 1
 	} else {
 		p.Column++
 	}

reader.go

@@ -18,7 +18,7 @@ func New(r io.Reader) *Reader {
 	return &Reader{
 		buf: ds.NewArrayStack[posRune](),
 		src: bufio.NewReader(r),
-		pos: &Position{},
+		pos: &Position{Index: 0, Line: 1, Column: 1},
 	}
 }
 
@@ -176,15 +176,23 @@ func (r *Reader) PeekStringUntil(f ...RuneFunc) (string, error) {
 }
 
 // SkipUntil acts as StringUntil but discards the string
+// The rune for which that function returned false will be unread.
 func (r *Reader) SkipUntil(f ...RuneFunc) error {
 	_, err := r.StringUntil(f...)
-	return err
+	if err != nil {
+		return err
+	}
+	return r.UnreadRune()
 }
 
-// SkipWhile acts as StringWhile but discards the string
+// SkipWhile acts as StringWhile but discards the string.
+// The rune for which that function returned false will be unread.
 func (r *Reader) SkipWhile(f ...RuneFunc) error {
 	_, err := r.StringWhile(f...)
-	return err
+	if err != nil {
+		return err
+	}
+	return r.UnreadRune()
 }
 
 // ExpectRune returns true if any function returns true for the next rune read from r