Eliminate a bunch of allocations

1 files changed, 45 insertions, 0 deletions

diff --git a/state.go b/state.go
new file mode 100644
index 0000000..f8df3f1
--- /dev/null
+++ b/state.go
@@ -0,0 +1,45 @@
+package parsec
+
+import "fmt"
+
+type Error struct {
+	pos      int
+	Expected string
+}
+
+func (e Error) Pos() int      { return e.pos }
+func (e Error) Error() string { return fmt.Sprintf("offset %d: Expected %s", e.pos, e.Expected) }
+
+type State struct {
+	Input string
+	Pos   int
+	Error Error
+}
+
+func (s *State) Advance(i int) {
+	s.Pos += i
+}
+
+func (s *State) Get() string {
+	if s.Pos > len(s.Input) {
+		return ""
+	}
+	return s.Input[s.Pos:]
+}
+
+func (s *State) ErrorHere(expected string) {
+	s.Error.pos = s.Pos
+	s.Error.Expected = expected
+}
+
+func (s *State) ClearError() {
+	s.Error.Expected = ""
+}
+
+func (s *State) Errored() bool {
+	return s.Error.Expected != ""
+}
+
+func InputString(input string) *State {
+	return &State{Input: input}
+}