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index.html
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<!DOCTYPE html>
<html>
<head>
<title>pest. The Elegant Parser</title>
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<link rel="stylesheet" type="text/css" href="style.css">
<link href="https://fonts.googleapis.com/css?family=Quicksand:300,400,700" rel="stylesheet">
<link href="https://fonts.googleapis.com/css?family=Space+Mono:400,700" rel="stylesheet">
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</head>
<body>
<div class="container-main">
<div class="bar-links bar-links-left">
<div><a href="https://github.com/pest-parser/pest">GitHub</a></div>
<div><a href="https://plugins.jetbrains.com/plugin/12046-pest">IDEA Plugin</a></div>
</div>
<div class="bar-links bar-links-right">
<div><a href="book">Book</a></div>
<div><a href="https://docs.rs/pest">Docs</a></div>
</div>
<img class="logo logo-bloom" src="assets/pest-logo.svg">
<img class="logo" src="assets/pest-logo.svg">
<a class="button-try" href="#editor">Try it here!</a>
<div class="banner-features"></div>
<div class="content features">
<div class="illustration">
<code class="sample">
<span>vals</span><span>.</span><span>push</span><span>(</span><span>3</span><span>)</span><span>;</span>
</code>
</br>
<code class="token">
{statement}
</code>
</div>
<h1>pest. The Elegant Parser</h1>
<p>
pest is a general purpose parser written in Rust with a focus on
<strong>accessibility</strong>, <strong>correctness</strong>, and
<strong>performance</strong>. It uses
<a href="https://en.wikipedia.org/wiki/Parsing_expression_grammar">
parsing expression grammars (or PEG)</a> as input, which are similar
in spirit to regular expressions, but which offer the enhanced
expressivity needed to parse complex languages.
</p>
<div class="feature-grid">
<div class="feature">
<h2>Accessibility</h2>
<p>
Grammar-generated parsers are both easier to use and maintain than
their hand-written counterparts.
</p>
</div>
<div>
<h2>Correctness</h2>
<p>
Grammars offer better correctness guarantees, and issues can be
solved declaratively in the grammar itself. Rust's memory safety
further limits the amount of damage bugs can do.
</p>
</div>
<div class="feature">
<h2>Performance</h2>
<p>
High-level static analysis and careful low-level implementation
build a solid foundation on which serious performance tuning is
possible.
</p>
</div>
</div>
</div>
<div class="content example">
<h2>Example</h2>
<p>
The following is an example of a grammar for a list of alpha-numeric
identifiers where the first identifier does not start with a digit:
</p>
<code class="code-block"><span class="ident">alpha</span> = { <span class="string">'a'</span><span class="op">..</span><span class="string">'z'</span> <span class="op">|</span> <span class="string">'A'</span><span class="op">..</span><span class="string">'Z'</span> }
<span class="ident">digit</span> = { <span class="string">'0'</span><span class="op">..</span><span class="string">'9'</span> }
<span class="ident">ident</span> = { (<span class="ident">alpha</span> <span class="op">|</span> <span class="ident">digit</span>)<span class="op">+</span> }
<span class="ident">ident_list</span> = <span class="mod">_</span>{ <span class="op">!</span><span class="ident">digit</span> <span class="op">~</span> <span class="ident">ident</span> <span class="op">~</span> (<span class="string">" "</span> <span class="op">~</span> <span class="ident">ident</span>)<span class="op">+</span> }
<span class="comment">// ^</span>
<span class="comment">// ident_list rule is silent (produces no tokens or error reports)</span></code>
<p>
Grammars are saved in separate <code>.pest</code> files which are
never mixed with procedural code. This results in an always up-to-date
formalization of a language that is easy to read and maintain.
</p>
</br>
<h2>Meaningful error reporting</h2>
<p>
Based on the grammar definition, the parser also includes automatic
error reporting. For the example above, the input <code>"123"</code>
will result in:
</p>
<code class="code-block">thread 'main' panicked at ' --> 1:1
<span class="comment">|</span>
1 <span class="comment">|</span> <span class="string">123</span>
<span class="comment">| ^---</span>
<span class="comment">|</span>
= <span class="op">unexpected digit</span>', src/main.rs:12</code>
<p>
while <code>"ab *"</code> will result in:
</p>
<code class="code-block">thread 'main' panicked at ' --> 1:1
<span class="comment">|</span>
1 <span class="comment">|</span> <span class="string">ab *</span>
<span class="comment">| ^---</span>
<span class="comment">|</span>
= <span class="op">expected ident</span>', src/main.rs:12</code>
</br>
</br>
</div>
<div class="banner-benchmark"></div>
<div class="content benchmark">
<h2>Measurements</h2>
<p>
Performance measurements place a pest-generated JSON parser in
somewhere below an optimized JSON parsers,
<a href="https://github.com/serde-rs/serde">serde</a>, and a static
native-speed parser, <a href="https://github.com/Geal/nom">nom</a>.
</p>
<div class="chart">
<div class="chart-label"><p class="chart-label-pest">pest</p></div>
<div class="chart-label"><p class="chart-label-nom">nom</p></div>
<div class="chart-label"><p class="chart-label-serde">serde</p></div>
<div class="chart-border chart-border-1"></div>
<div class="chart-border chart-border-2"></div>
<div class="chart-border chart-border-3"></div>
<div class="chart-bar chart-bar-pest">
<div class="chart-bar-hidden">
<p>150</p>
</div>
</div>
<div class="chart-bar chart-bar-nom">
<div class="chart-bar-hidden">
<p>366</p>
</div>
</div>
<div class="chart-bar chart-bar-serde">
<div class="chart-bar-hidden">
<p>472</p>
</div>
</div>
<div class="chart-value chart-value-0"><p>0MB/s</p></div>
<div class="chart-value chart-value-250"><p>250MB/s</p></div>
<div class="chart-value chart-value-500"><p>500MB/s</p></div>
</div>
</div>
<div class="content editor">
<a name="editor"><h2>Editor</h2></a>
<button onclick="wideMode()" id="modeBtn">Wide Mode</button>
<button onclick="share()">Share</button><a class="direct-link"></a>
<div class="editor-grid">
<textarea rows="15" class="editor-grammar grammar-area"></textarea>
<div class="editor-input">
<textarea rows="3" placeholder="Input" class="editor-input-text"></textarea>
<select disabled class="editor-input-select">
<option>...</option>
</select>
</div>
<div class="output-wrapper">
<textarea rows="7" placeholder="Output" readonly class="editor-output"></textarea>
</div>
</div>
</div>
</div>
<script src="https://cdnjs.cloudflare.com/ajax/libs/split.js/1.5.11/split.min.js"></script>
<script type="module">
import init, { lint } from './pest_site.js';
window.lint = lint;
async function run() {
await init();
}
run();
</script>
<script src="codemirror/lib/codemirror.js"></script>
<script src="codemirror/addon/display/placeholder.js"></script>
<script src="codemirror/addon/lint/lint.js"></script>
<link rel="stylesheet" href="codemirror/addon/lint/lint.css">
<script src="codemirror/addon/mode/simple.js"></script>
<link rel="stylesheet" href="codemirror/lib/codemirror.css">
<script type="text/javascript">
const editorDom = document.querySelector(".editor");
const gridDom = document.querySelector(".editor-grid");
const inputDom = document.querySelector(".editor-input");
const outputDom = document.querySelector(".editor-output");
const modeBtn = document.querySelector("#modeBtn");
let windowHeight = window.innerHeight;
var current_data = null;
CodeMirror.defineSimpleMode("pest", {
start: [
{regex: /"/, token: "string", next: "string"},
{regex: /'(?:[^'\\]|\\(?:[nrt0'"]|x[\da-fA-F]{2}|u\{[\da-fA-F]{6}\}))'/, token: "string"},
{regex: /\/\/.*/, token: "comment"},
{regex: /\d+/, token: "number"},
{regex: /[~|*+?&!]|(\.\.)/, token: "operator"},
{regex: /[a-zA-Z_]\w*/, token: "variable"},
{regex: /=/, next: "mod"}
],
mod: [
{regex: /\{/, next: "start"},
{regex: /[_@!$]/, token: "operator-2"},
],
string: [
{regex: /"/, token: "string", next: "start"},
{regex: /(?:[^\\"]|\\(?:.|$))*/, token: "string"}
],
meta: {
dontIndentStates: ["comment"],
lineComment: "//"
}
});
CodeMirror.registerHelper("lint", "pest", function(text) {
if (window.lint) {
var doc = CodeMirror.Doc(text);
var errors = window.lint(text);
var mapped = [];
for (var i = 0; i < errors.length; i++) {
var from = doc.clipPos(eval("CodeMirror.Pos" + errors[i].get("from")));
var to = doc.clipPos(eval("CodeMirror.Pos" + errors[i].get("to")));
if (from.line === to.line && from.ch === to.ch) {
to.ch += 1;
to = doc.clipPos(to);
}
if (from.line === to.line && from.ch === to.ch) {
from.ch -= 1;
from = doc.clipPos(from);
}
mapped.push({
message: errors[i].get("message"),
from: from,
to: to
});
}
return mapped;
} else {
return [];
}
});
var grammar = document.getElementsByClassName("editor-grammar")[0];
var myCodeMirror = CodeMirror.fromTextArea(grammar, {
mode: "pest",
lint: "pest",
theme: "pest",
placeholder: "Grammar",
});
var url = new URL(window.location.href);
var bin = url.searchParams.get("bin");
if (bin) {
var http = new XMLHttpRequest();
var url = "https://api.myjson.com/bins/" + bin;
http.open("GET", url, true);
http.onreadystatechange = function() {
if (http.readyState === 4 && http.status === 200) {
var data = JSON.parse(http.responseText);
current_data = data;
myCodeMirror.setValue(data["grammar"]);
}
}
http.send(null);
}
function set_current_data() {
if (current_data) {
var select = document.getElementsByClassName("editor-input-select")[0];
for (var i = 0; i < select.options.length; i++) {
if (select.options[i].value === current_data["rule"]) {
select.selectedIndex = i;
var event = new Event('change');
select.dispatchEvent(event);
break;
}
}
var input = document.getElementsByClassName("editor-input-text")[0];
input.value = current_data["input"];
current_data = null;
}
}
function share() {
var data = {};
var select = document.getElementsByClassName("editor-input-select")[0];
data["grammar"] = myCodeMirror.getValue();
data["input"] = document.getElementsByClassName("editor-input-text")[0].value;
data["rule"] = select.options[select.selectedIndex].value;
var http = new XMLHttpRequest();
var url = "https://api.myjson.com/bins";
http.open("POST", url, true);
http.setRequestHeader('Content-Type', 'application/json; charset=UTF-8');
http.onreadystatechange = function() {
if (http.readyState === 4 && http.status === 201) {
var url = JSON.parse(http.responseText)["uri"];
var tokens = url.split("/");
var bin = tokens[tokens.length - 1];
var link = document.getElementsByClassName("direct-link")[0];
link.href = "https://pest-parser.github.io/?bin=" + bin + "#editor";
link.text = "direct link";
}
};
http.send(JSON.stringify(data));
}
let split = null;
let sizes = localStorage.getItem('split-sizes');
if (sizes) {
sizes = JSON.parse(sizes)
} else {
sizes = [33, 33, 33] // default sizes
}
function makeResizable(wideMode) {
if (wideMode) {
split = Split(['.CodeMirror', '.editor-input', '.output-wrapper'], {
sizes,
onDragEnd: function(_sizes) {
sizes = _sizes;
localStorage.setItem('split-sizes', JSON.stringify(sizes))
},
})
} else {
if (split) {
split.destroy();
}
}
}
function wideMode() {
modeBtn.onclick = restore;
modeBtn.innerText = "Normal Mode";
inputDom.classList.add("wide-input");
editorDom.classList.add("wide-editor");
gridDom.classList.add("flex-editor");
const upperHeight = document.querySelector('#modeBtn').scrollHeight + 30;
gridDom.setAttribute('style', `height: ${windowHeight - upperHeight}px`);
myCodeMirror.setSize(null, outputDom.clientHeight - 20);
makeResizable(true);
window.scrollTo(0,document.body.scrollHeight);
}
function restore() {
modeBtn.onclick = wideMode;
modeBtn.innerText = "Wide Mode";
inputDom.classList.remove("wide-input");
editorDom.classList.remove("wide-editor");
gridDom.classList.remove("flex-editor");
outputDom.setAttribute("rows", 7);
myCodeMirror.setSize(null, outputDom.clientHeight);
makeResizable(false);
}
</script>
</body>
</html>