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README.md: rework instructions to show how to use 'peg' via 'go tool' #193

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38 changes: 18 additions & 20 deletions README.md
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A [Parsing Expression Grammar](https://en.wikipedia.org/wiki/Parsing_expression_grammar) ( hence `peg`) is a way to create grammars similar in principle to [regular expressions](https://en.wikipedia.org/wiki/Regular_expression) but which allow better code integration. Specifically, `peg` is an implementation of the [Packrat](https://en.wikipedia.org/wiki/Parsing_expression_grammar#Implementing_parsers_from_parsing_expression_grammars) parser generator originally implemented as [peg/leg](https://www.piumarta.com/software/peg/) by [Ian Piumarta](https://www.piumarta.com/cv/) in C. A Packrat parser is a "descent recursive parser" capable of backtracking and negative look-ahead assertions which are problematic for regular expression engines.

## Installation
## PEG file syntax

```
go install github.com/pointlander/peg@latest
```
See [peg-file-syntax.md](docs/peg-file-syntax.md)


## Usage

### Build executable

1. Add `peg` as a [tool](https://go.dev/doc/modules/managing-dependencies#tools) in your Go module:
```console
$ go get -tool github.com/pointlander/peg@main
```
go generate && go build
```

### Help

2. Create your `mygrammar.peg` file (see [doc](docs/peg-file-syntax.md))
3. Add a `//go:generate` line in a Go source of your package (idiom is `doc.go`):
```go
//go:generate go tool peg mygrammar.peg
```
./peg -h
3. Run `go generate` to generate `mygrammar.peg.go` from `mygrammar.peg`
```console
$ go generate
```


### Example

This creates the file `peg.peg.go`:
```
./peg -inline -switch peg.peg
$ go tool peg -inline -switch peg.peg
```


## PEG file syntax

See [peg-file-syntax.md](docs/peg-file-syntax.md)

### Help
```
$ go tool peg -h
```

## Development

### Requirements

* [Golang](https://golang.org/doc/install), see [go.mod](go.mod) for version
* [Golang](https://go.dev/doc/install), see [go.mod](go.mod) for version
* [golangci-lint latest version](https://github.com/golangci/golangci-lint#install) (v2 or later)
* [Bash 3.2.x or higher](https://www.gnu.org/software/bash)

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