feat: iterator.While, slimmed comments in saccharine

pkg/iterator/iterator.go

@@ -81,6 +81,17 @@ func (i Iterator[T]) Done() bool {
 	return i.index == len(i.items)
 }
 
+// While increments the iterator as long as the current item satisfies the
+// predicate. The first item that does not match is left unconsumed.
+func (i *Iterator[T]) While(fn func(T) bool) {
+	for !i.Done() {
+		if !fn(i.MustGet()) {
+			return
+		}
+		i.Forward()
+	}
+}
+
 // Try attempts to perform an operation using the iterator. If the operation
 // succeeds, the iterator is updated. If the operation fails, the iterator is
 // rolled back, and an error is returned.

pkg/saccharine/scan.go

@@ -47,18 +47,7 @@ func scanToken(i *iterator.Iterator[rune]) (*Token, error) {
 		return token.New(TokenHardBreak, index), nil
 	case letter == '#':
 		// Skip everything until the next newline or EOF.
-		for !i.Done() {
-			r, err := i.Next()
-			if err != nil {
-				return nil, fmt.Errorf("error while parsing comment: %w", err)
-			}
-
-			if r == '\n' {
-				// Put the newline back so it can be processed as a soft break.
-				i.Back()
-				break
-			}
-		}
+		i.While(func(r rune) bool { return r != '\n' })
 		return nil, nil
 	case unicode.IsSpace(letter):
 		return nil, nil