From 2d3c8748bee9f50f43e2e4705fd34cc7bc062f80 Mon Sep 17 00:00:00 2001
From: Brandon Dyck <brandon@dyck.us>
Date: Tue, 17 Sep 2024 21:40:47 -0600
Subject: [PATCH] Implemented csexp.Parse

---
 csexp/sexp.go | 76 +++++++++++++++++++++++++++++++++++++++++++++++++--
 go.mod        |  9 ++++--
 go.sum        |  4 +--
 3 files changed, 83 insertions(+), 6 deletions(-)

diff --git a/csexp/sexp.go b/csexp/sexp.go
index e9dd54c..6f696e9 100644
--- a/csexp/sexp.go
+++ b/csexp/sexp.go
@@ -2,10 +2,15 @@ package csexp
 
 import (
 	"bytes"
+	"errors"
 	"fmt"
 	"io"
 	"slices"
+	"strconv"
 
+	"git.codemonkeysoftware.net/b/gigaparsec"
+	pbytes "git.codemonkeysoftware.net/b/gigaparsec/bytes"
+	"git.codemonkeysoftware.net/b/gigaparsec/cursor"
 	"git.codemonkeysoftware.net/b/peachy-go/shortcircuit"
 )
 
@@ -82,6 +87,73 @@ func (l List) Clone() Sexp {
 	return l2
 }
 
-func Parse(data []byte) (Sexp, error) {
-	return nil, nil
+var parseLength = gigaparsec.Map(pbytes.Regexp(`0|[1-9]\d*`), func(s string) uint64 {
+	n, err := strconv.ParseUint(s, 10, 64)
+	if err != nil {
+		panic(err)
+	}
+	return n
+})
+
+func acceptN(n uint64) gigaparsec.Parser[byte, []byte] {
+	expected := fmt.Sprintf("%d bytes", n)
+	return func(s gigaparsec.State[byte]) (gigaparsec.Result[byte, []byte], error) {
+		if n == 0 {
+			return gigaparsec.Succeed[byte, []byte](true, nil, s, gigaparsec.MessageOK(s.Pos())), nil
+		}
+		dst := make([]byte, n)
+		_, next, err := s.Read(dst)
+		if errors.Is(err, io.EOF) {
+			return gigaparsec.Fail[byte, []byte](false, gigaparsec.MessageEnd(s.Pos(), expected)), nil
+		}
+		if err != nil {
+			return gigaparsec.Result[byte, []byte]{}, err
+		}
+		return gigaparsec.Succeed(true, dst, next, gigaparsec.MessageOK(s.Pos())), nil
+	}
+}
+
+var parseAtom = gigaparsec.Map(gigaparsec.Bind2(
+	parseLength,
+	gigaparsec.Pipe[byte, byte, uint64](gigaparsec.Match[byte](':')),
+	acceptN,
+), func(s []byte) Sexp { return Atom(s) })
+
+func parseSexp(input gigaparsec.State[byte]) (gigaparsec.Result[byte, Sexp], error) {
+	return gigaparsec.Choose(parseAtom, parseList)(input)
+}
+
+func parseRestOfList(input gigaparsec.State[byte]) (gigaparsec.Result[byte, []Sexp], error) {
+	return gigaparsec.Choose(
+		gigaparsec.Map(gigaparsec.Match[byte](')'), func(byte) []Sexp { return nil }),
+		gigaparsec.Bind(
+			parseSexp,
+			func(s Sexp) gigaparsec.Parser[byte, []Sexp] {
+				return gigaparsec.Map(
+					parseRestOfList,
+					func(rest []Sexp) []Sexp { return append([]Sexp{s}, rest...) },
+				)
+			},
+		),
+	)(input)
+}
+
+func parseList(input gigaparsec.State[byte]) (gigaparsec.Result[byte, Sexp], error) {
+	return gigaparsec.Map(gigaparsec.Seq2(
+		gigaparsec.Match[byte]('('),
+		parseRestOfList,
+		func(_ byte, rest []Sexp) []Sexp { return rest },
+	), func(sexps []Sexp) Sexp { return List(sexps) })(input)
+}
+
+func Parse(data []byte) (Sexp, error) {
+	result, err := parseSexp(gigaparsec.MakeState(cursor.NewSlice(data)))
+	if err != nil {
+		return nil, fmt.Errorf("csexp.Parse: %w", err)
+	}
+	if failed, _, msg := result.Failed(); failed {
+		return nil, fmt.Errorf("csexp.Parse: %v", msg)
+	}
+	_, _, sexp, _, _ := result.Succeeded()
+	return sexp, nil
 }
diff --git a/go.mod b/go.mod
index 78d0c2a..061b6c9 100644
--- a/go.mod
+++ b/go.mod
@@ -1,10 +1,13 @@
 module git.codemonkeysoftware.net/b/peachy-go
 
-go 1.22.1
+go 1.23
+
+toolchain go1.23.0
 
 require (
+	git.codemonkeysoftware.net/b/gigaparsec v0.0.0-20240917174243-4fa3c2a46611
 	github.com/pkg/browser v0.0.0-20240102092130-5ac0b6a4141c
-	github.com/shoenig/test v1.9.0
+	github.com/shoenig/test v1.11.0
 	pgregory.net/rapid v1.1.0
 	zombiezen.com/go/sqlite v1.3.0
 )
@@ -22,3 +25,5 @@ require (
 	modernc.org/memory v1.7.2 // indirect
 	modernc.org/sqlite v1.29.1 // indirect
 )
+
+replace git.codemonkeysoftware.net/b/gigaparsec v0.0.0-20240917174243-4fa3c2a46611 => ../gigaparsec
diff --git a/go.sum b/go.sum
index 939ba2a..22fc0bd 100644
--- a/go.sum
+++ b/go.sum
@@ -12,8 +12,8 @@ github.com/pkg/browser v0.0.0-20240102092130-5ac0b6a4141c h1:+mdjkGKdHQG3305AYmd
 github.com/pkg/browser v0.0.0-20240102092130-5ac0b6a4141c/go.mod h1:7rwL4CYBLnjLxUqIJNnCWiEdr3bn6IUYi15bNlnbCCU=
 github.com/remyoudompheng/bigfft v0.0.0-20230129092748-24d4a6f8daec h1:W09IVJc94icq4NjY3clb7Lk8O1qJ8BdBEF8z0ibU0rE=
 github.com/remyoudompheng/bigfft v0.0.0-20230129092748-24d4a6f8daec/go.mod h1:qqbHyh8v60DhA7CoWK5oRCqLrMHRGoxYCSS9EjAz6Eo=
-github.com/shoenig/test v1.9.0 h1:PWtSP8Ty2N0F+Ndh4p0a8SOofFmTEIX/nYh/c3vRCbo=
-github.com/shoenig/test v1.9.0/go.mod h1:UxJ6u/x2v/TNs/LoLxBNJRV9DiwBBKYxXSyczsBHFoI=
+github.com/shoenig/test v1.11.0 h1:NoPa5GIoBwuqzIviCrnUJa+t5Xb4xi5Z+zODJnIDsEQ=
+github.com/shoenig/test v1.11.0/go.mod h1:UxJ6u/x2v/TNs/LoLxBNJRV9DiwBBKYxXSyczsBHFoI=
 golang.org/x/sys v0.0.0-20220811171246-fbc7d0a398ab/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/sys v0.1.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/sys v0.16.0 h1:xWw16ngr6ZMtmxDyKyIgsE93KNKz5HKmMa3b8ALHidU=