go-parsekit/examples/example_helloManyStateParser_test.go

// In this example, a parser is created that is able to parse input that looks
// like "Hello, <name>!", and that extracts the name from it.
//
// This implementation uses a state-based Parser for it, and it does not
// implement any custom parser/combinator Handler functions. Note that
// things are much easier to implement using custom Handlers (see the
// helloParserCombinator example for this). Doing this fully parser-based
// implementation is mainly for your learning pleasure.
//
// One big difference between the parser/combinator-based example and this one,
// is that this parser reports errors much more fine-grained. This might or
// might not be useful for your specific use case. If you need error reporting
// like this, then also take a look at the helloSingleState example, which does
// the same thing as this version, only more concise.

package examples

import (
	"fmt"
	"strings"

	"git.makaay.nl/mauricem/go-parsekit/parse"
	"git.makaay.nl/mauricem/go-parsekit/tokenize"
)

func Example_helloWorldUsingParser1() {
	for i, input := range []string{
		"Oh!",
		"Hello, world!",
		"HELLO ,Johnny!",
		"hello , Bob123!",
		"hello Pizza!",
		"",
		" ",
		"hello",
		"hello,",
		"hello , ",
		"hello , Droopy",
		"hello , Droopy!",
		"hello , \t \t Droopy \t !",
		"Oh no!",
		"hello,!",
		"hello, \t!",
	} {
		name, err := (&helloparser1{}).Parse(input)
		if err != nil {
			fmt.Printf("[%d] Input: %q Error: %s\n", i, input, err)
		} else {
			fmt.Printf("[%d] Input: %q Output: %s\n", i, input, name)
		}
	}
	// [0] Input: "Oh!" Error: unexpected input (expected hello)
	// [1] Input: "Hello, world!" Output: world
	// [2] Input: "HELLO ,Johnny!" Output: Johnny
	// [3] Input: "hello , Bob123!" Output: Bob123
	// [4] Input: "hello Pizza!" Error: unexpected input (expected comma)
	// [5] Input: "" Error: unexpected end of file (expected hello)
	// [6] Input: " " Error: unexpected input (expected hello)
	// [7] Input: "hello" Error: unexpected end of file (expected comma)
	// [8] Input: "hello," Error: unexpected end of file (expected name)
	// [9] Input: "hello , " Error: unexpected end of file (expected name)
	// [10] Input: "hello , Droopy" Error: unexpected end of file (expected exclamation mark)
	// [11] Input: "hello , Droopy!" Output: Droopy
	// [12] Input: "hello , \t \t Droopy \t !" Output: Droopy
	// [13] Input: "Oh no!" Error: unexpected input (expected hello)
	// [14] Input: "hello,!" Error: The name cannot be empty
	// [15] Input: "hello, \t!" Error: The name cannot be empty
}

// ―――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――
// Implementation of the parser
// ―――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――

type helloparser1 struct {
	greetee string
}

func (h *helloparser1) Parse(input string) (string, error) {
	parseHello := parse.New(h.start)
	err := parseHello(input)
	return h.greetee, err
}

func (h *helloparser1) start(p *parse.API) {
	a := tokenize.A
	if p.Skip(a.StrNoCase("hello")) {
		p.Handle(h.comma)
	} else {
		p.Expected("hello")
	}
}

func (h *helloparser1) comma(p *parse.API) {
	a := tokenize.A
	p.Skip(a.Blanks)
	if p.Skip(a.Comma) {
		p.Handle(h.startName)
	} else {
		p.Expected("comma")
	}
}

func (h *helloparser1) startName(p *parse.API) {
	a := tokenize.A
	p.Skip(a.Blanks)
	if p.Peek(a.AnyRune) {
		p.Handle(h.name)
	} else {
		p.Expected("name")
	}
}

func (h *helloparser1) name(p *parse.API) {
	a := tokenize.A
	switch {
	case p.Peek(a.Excl):
		p.Handle(h.exclamation)
	case p.Accept(a.AnyRune):
		h.greetee += p.Result.String()
		p.Handle(h.name)
	default:
		p.Expected("exclamation mark")
	}
}

func (h *helloparser1) exclamation(p *parse.API) {
	a := tokenize.A
	if p.Skip(a.Excl) {
		p.Handle(h.end)
	} else {
		p.Expected("exclamation")
	}
}

// Here we could have used p.ExpectEndOfFile() as well, but a slightly
// different route was taken to implement a more friendly 'end of greeting'
// error message.
func (h *helloparser1) end(p *parse.API) {
	var a = tokenize.A
	if !p.Skip(a.EndOfFile) {
		p.Expected("end of greeting")
		return
	}

	h.greetee = strings.TrimSpace(h.greetee)
	if h.greetee == "" {
		p.SetError("The name cannot be empty")
	} else {
		p.Stop()
	}
}