Added canonical sexps sans parsing

csexp/sexp.go

@@ -0,0 +1,87 @@
+package csexp
+
+import (
+	"bytes"
+	"fmt"
+	"io"
+	"slices"
+
+	"git.codemonkeysoftware.net/b/peachy-go/shortcircuit"
+)
+
+type Sexp interface {
+	isSexp()
+	WriteTo(w io.Writer) (n int64, err error)
+	String() string
+	Equal(Sexp) bool
+	Clone() Sexp
+}
+
+type Atom []byte
+
+func (a Atom) isSexp() {}
+
+func (a Atom) WriteTo(w io.Writer) (int64, error) {
+	if scw, ok := w.(*shortcircuit.Writer); ok && scw.Failed() {
+		return 0, nil
+	}
+
+	n, err := fmt.Fprintf(w, "%d:%s", len(a), []byte(a))
+	return int64(n), err
+}
+
+func (a Atom) String() string {
+	var buf bytes.Buffer
+	a.WriteTo(&buf)
+	return buf.String()
+}
+
+func (a Atom) Equal(s Sexp) bool {
+	a2, ok := s.(Atom)
+	return ok && bytes.Equal([]byte(a), []byte(a2))
+}
+
+func (a Atom) Clone() Sexp {
+	return Atom(bytes.Clone([]byte(a)))
+}
+
+type List []Sexp
+
+func (l List) isSexp() {}
+
+func (l List) WriteTo(w io.Writer) (int64, error) {
+	scw := shortcircuit.EnsureWriter(w)
+	if scw.Failed() {
+		return 0, nil
+	}
+
+	io.WriteString(scw, "(")
+	for _, child := range l {
+		child.WriteTo(scw)
+	}
+	io.WriteString(scw, ")")
+	return scw.Status()
+}
+
+func (l List) String() string {
+	var buf bytes.Buffer
+	l.WriteTo(&buf)
+	return buf.String()
+}
+
+func (l List) Equal(s Sexp) bool {
+	l2, ok := s.(List)
+	return ok && slices.EqualFunc(l, l2, Sexp.Equal)
+}
+
+func (l List) Clone() Sexp {
+	l2 := make(List, len(l))
+	for i, child := range l {
+		l2[i] = child.Clone()
+	}
+	return l2
+}
+
+func Parse(data []byte) (Sexp, error) {
+	return nil, nil
+}