docs: add godoc examples, extend the basic example and map encoding/json

Assisted-by: GLM 5.3 Flash

docs/API.md

@@ -797,6 +797,29 @@ sequenceDiagram
     Marshal-->>Caller: bytes, error
 ```
 
+## Coming from encoding/json
+
+The API follows the shapes encoding/json made familiar, with the differences
+TOML asks for:
+
+| encoding/json | interpres | Notes |
+|---|---|---|
+| `json.Unmarshal(data, v)` | `Unmarshal(data, v)` | the same shape; the value mapping is TOML's |
+| `json.Marshal(v)` | `Marshal(v)` | the same shape; the output is TOML 1.1 |
+| `json.MarshalAppend(buf, v)` | `MarshalAppend(buf, v)` | the same shape |
+| `(*json.Decoder).DisallowUnknownFields` | `(*Decoder).DisallowUnknownFields` | the same effect; the one-shot form is `UnmarshalWithOptions` |
+| `json.Number`, `(*json.Decoder).UseNumber` | `Number`, `(*Decoder).UseNumber` | the TOML literal carries its radix and separators, so `0x1f` stays `0x1f` |
+| `json.MarshalIndent` | none | TOML is the presentation format; the `-json` mode of interpres-decode prints plain JSON |
+| tag `json:"name,omitempty"` | tag `toml:"name,omitempty"` | the empty-value rules match encoding/json as of 2.0 |
+| tag `json:"name,omitzero"` | tag `toml:"name,omitzero"` | the same, `IsZero()` honoured |
+| tag `json:"name,inline"` (v2) | tag `toml:"name,inline"` | forces the inline table form on encode |
+| `json.Marshaler` (`MarshalJSON`) | `Marshaler` (`MarshalTOML`) | the TOML method returns a value the encoder renders, not bytes |
+| `json.Unmarshaler` (`UnmarshalJSON`) | `Unmarshaler` (`UnmarshalTOML`) | the data arrives decoded, not as bytes |
+| `encoding.TextMarshaler`, `TextUnmarshaler` | honoured, the same | a type that renders itself as text becomes a TOML string, both ways |
+| `*json.UnmarshalTypeError` | `*DecodeError` | the path is segments with a `String()` renderer, not a dotted string |
+| `*json.SyntaxError` | `*SyntaxError` | the TOML error adds the byte `Offset` and the `Column` to the line |
+| context support | `*Context` variants of every entry point | encoding/json has none |
+
 ## Types
 
 ### `type SyntaxError struct{ Line, Offset, Column int; Msg string }`

example_test.go

@@ -0,0 +1,103 @@
+// Copyright (c) 2026 Petr Balvín <opensource@petrbalvin.org> (https://petrbalvin.org)
+// SPDX-License-Identifier: MIT
+
+package interpres_test
+
+import (
+	"fmt"
+	"log"
+
+	"sourcedock.dev/petrbalvin/interpres/v2"
+)
+
+func ExampleParse() {
+	const doc = `
+title = "interpres"
+
+[server]
+host = "127.0.0.1"
+port = 9090
+`
+	d, err := interpres.Parse([]byte(doc))
+	if err != nil {
+		log.Fatal(err)
+	}
+	for _, key := range d.Root().Keys() { // written order, not sorted
+		entry, _ := d.Root().Get(key)
+		fmt.Println(key, "=", entry.Value())
+	}
+	// Output:
+	// title = interpres
+	// server = map[host:127.0.0.1 port:9090]
+}
+
+func ExampleUnmarshal() {
+	type Config struct {
+		Host string `toml:"host"`
+		Port int    `toml:"port"`
+	}
+	var cfg Config
+	err := interpres.Unmarshal([]byte("host = \"db\"\nport = 5432\n"), &cfg)
+	if err != nil {
+		log.Fatal(err)
+	}
+	fmt.Println(cfg.Host, cfg.Port)
+	// Output: db 5432
+}
+
+func ExampleMarshal() {
+	type Server struct {
+		Host string `toml:"host"`
+		Port int    `toml:"port"`
+	}
+	type Config struct {
+		Title  string `toml:"title"`
+		Server Server `toml:"server"`
+	}
+	out, err := interpres.Marshal(Config{
+		Title:  "demo",
+		Server: Server{Host: "127.0.0.1", Port: 9090},
+	})
+	if err != nil {
+		log.Fatal(err)
+	}
+	fmt.Printf("%s", out)
+	// Output:
+	// title = "demo"
+	//
+	// [server]
+	// host = "127.0.0.1"
+	// port = 9090
+}
+
+func ExampleDecoder() {
+	var tree map[string]any
+	err := interpres.NewDecoder().
+		DisallowUnknownFields().
+		UseNumber().
+		Decode([]byte("rate = 1_000\n"), &tree)
+	if err != nil {
+		log.Fatal(err)
+	}
+	fmt.Println(tree["rate"], string(tree["rate"].(interpres.Number)))
+	// Output: 1_000 1_000
+}
+
+func ExampleEncoder() {
+	type Config struct {
+		Title  string            `toml:"title"`
+		Extras map[string]string `toml:"extras,inline"`
+	}
+	out, err := interpres.NewEncoder().
+		Layout(interpres.LayoutKindDeclaration).
+		LiteralMultiline(80).
+		InlineTables(40).
+		Marshal(Config{Title: "demo", Extras: map[string]string{"b": "two", "a": "one"}})
+	if err != nil {
+		log.Fatal(err)
+	}
+	fmt.Printf("%s", out)
+	// Output:
+	// title = "demo"
+	// extras = {a = "one", b = "two"}
+}

examples/basic/main.go

@@ -8,6 +8,7 @@
 package main
 
 import (
+	"errors"
 	"fmt"
 	"io"
 	"os"
@@ -39,13 +40,16 @@ admin = false
 
 // Config mirrors the document above. The Server field is a named struct so
 // the reader sees explicit subtable boundaries; Users is a slice of named
-// structs so the array-of-tables path is exercised.
+// structs so the array-of-tables path is exercised. Retries carries the
+// `omitzero` tag option: a zero value of the field's type drops from the
+// output, and a `time.Duration` zero is zero nanoseconds.
 type Config struct {
-	Title    string    `toml:"title"`
-	Launched time.Time `toml:"launched"`
-	Debug    bool      `toml:"debug"`
-	Server   Server    `toml:"server"`
-	Users    []User    `toml:"users"`
+	Title    string        `toml:"title"`
+	Launched time.Time     `toml:"launched"`
+	Debug    bool          `toml:"debug"`
+	Server   Server        `toml:"server"`
+	Users    []User        `toml:"users"`
+	Retries  time.Duration `toml:"retries,omitzero"`
 }
 
 type Server struct {
@@ -147,5 +151,33 @@ func Run(stdout, stderr io.Writer) int {
 	fmt.Fprintf(stdout, "\n--- round-trip --- ok (title=%q, users=%d)\n",
 		roundTripped.Title, len(roundTripped.Users))
 
+	// Typed errors: a decode failure names the key path it failed at, and
+	// errors.AsType reaches the DecodeError to read the path and the cause
+	// separately, without parsing the message text.
+	bad := []byte("[[users]]\nname = \"x\"\nadmin = \"not-a-bool\"\n")
+	var badCfg Config
+	err = interpres.Unmarshal(bad, &badCfg)
+	if err == nil {
+		fmt.Fprintln(stderr, "expected a decode error")
+		return 1
+	}
+	if de, ok := errors.AsType[*interpres.DecodeError](err); ok {
+		fmt.Fprintf(stdout, "\n--- typed error --- path %s: %v\n", de.Path.String(), de.Err)
+	} else {
+		fmt.Fprintln(stderr, "expected a DecodeError")
+		return 1
+	}
+
+	// omitzero: the retries field carries the tag option and a zero duration,
+	// so the re-encoded config above simply has no retries line. Give it a
+	// value and the line appears.
+	cfg.Retries = 30 * time.Second
+	out3, err := interpres.Marshal(cfg)
+	if err != nil {
+		fmt.Fprintln(stderr, "marshal:", err)
+		return 1
+	}
+	fmt.Fprintf(stdout, "\n--- omitzero ---\n%s", out3)
+
 	return 0
 }