feat: json example (#395)

* feat: json example

* fix: Whitespace contains EOL in Json lexer

_examples/json/main.go

@@ -0,0 +1,86 @@
+// nolint: golint, dupl
+package main
+
+import (
+	"os"
+
+	"github.com/alecthomas/kong"
+
+	"github.com/alecthomas/participle/v2"
+	"github.com/alecthomas/participle/v2/lexer"
+)
+
+var (
+	jsonLexer = lexer.MustSimple([]lexer.SimpleRule{
+		{Name: "Comment", Pattern: `\/\/[^\n]*`},
+		{Name: "String", Pattern: `"(\\"|[^"])*"`},
+		{Name: "Number", Pattern: `[-+]?(\d*\.)?\d+`},
+		{Name: "Punct", Pattern: `[-[!@#$%^&*()+_={}\|:;"'<,>.?/]|]`},
+		{Name: "Null", Pattern: "null"},
+		{Name: "True", Pattern: "true"},
+		{Name: "False", Pattern: "false"},
+		{Name: "EOL", Pattern: `[\n\r]+`},
+		{Name: "Whitespace", Pattern: `[ \t]+`},
+	})
+
+	jsonParser = participle.MustBuild[Json](
+		participle.Lexer(jsonLexer),
+		participle.Unquote("String"),
+		participle.Elide("Whitespace", "EOL"),
+		participle.UseLookahead(2),
+	)
+
+	cli struct {
+		File string `arg:"" type:"existingfile" help:"File to parse."`
+	}
+)
+
+// Parse a Json string.
+func Parse(data []byte) (*Json, error) {
+	json, err := jsonParser.ParseBytes("", data)
+	if err != nil {
+		return nil, err
+	}
+	return json, nil
+}
+
+type Json struct {
+	Pos lexer.Position
+
+	Object *Object `parser:"@@ |"`
+	Array  *Array  `parser:"@@ |"`
+	Number *string `parser:"@Number |"`
+	String *string `parser:"@String |"`
+	False  *string `parser:"@False |"`
+	True   *string `parser:"@True |"`
+	Null   *string `parser:"@Null"`
+}
+
+type Object struct {
+	Pos lexer.Position
+
+	Pairs []*Pair `parser:"'{' @@ (',' @@)* '}'"`
+}
+
+type Pair struct {
+	Pos lexer.Position
+
+	Key   string `parser:"@String ':'"`
+	Value *Json  `parser:"@@"`
+}
+
+type Array struct {
+	Pos lexer.Position
+
+	Items []*Json `parser:"'[' @@ (',' @@)* ']'"`
+}
+
+func main() {
+	ctx := kong.Parse(&cli)
+	data, err := os.ReadFile(cli.File)
+	ctx.FatalIfErrorf(err)
+
+	res, err := Parse(data)
+	ctx.FatalIfErrorf(err)
+	ctx.Printf("res is: %v", res)
+}

_examples/json/main_test.go

@@ -0,0 +1,15 @@
+package main
+
+import (
+	"os"
+	"testing"
+
+	require "github.com/alecthomas/assert/v2"
+)
+
+func TestParse(t *testing.T) {
+	src, err := os.ReadFile("./test.json")
+	require.NoError(t, err)
+	_, err = Parse(src)
+	require.NoError(t, err)
+}

_examples/json/test.json

@@ -0,0 +1,11 @@
+{
+    "list": [1, 1.2, 1, -1, {"foo": "bar"}, true, false, null],
+    "object": {
+        "foo1": "bar2",
+        "foo2": true,
+        "foo3": false,
+        "foo4": null,
+        "foo5": 1,
+        "foo6": "ss"
+    }
+}