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index.html
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<html>
<head>
<meta charset="utf-8" />
<meta name="description" content="An Earley SPPF parser and visualizer" />
<meta name="keywords" content="Earley, SPPF" />
<meta name="viewport" content="width=device-width, initial-scale=1.0" />
<title>An Earley Parser Visualizer</title>
<link rel="preconnect" href="https://fonts.googleapis.com" />
<link rel="preconnect" href="https://fonts.gstatic.com" crossorigin />
<link
href="https://fonts.googleapis.com/css2?family=Inter&family=JetBrains+Mono&display=swap"
rel="stylesheet"
/>
<link rel="stylesheet" href="css/normalize.css" />
<link rel="stylesheet" href="css/style.css" />
<script src="https://unpkg.com/svg-pan-zoom@3.6.1/dist/svg-pan-zoom.min.js"></script>
<script src="scripts/viz.js"></script>
<script src="scripts/full.render.js"></script>
<script src="scripts/earley.js"></script>
</head>
<!-- Google tag (gtag.js) -->
<script async src="https://www.googletagmanager.com/gtag/js?id=G-7SN3NCBBWK"></script>
<script>
window.dataLayer = window.dataLayer || [];
function gtag(){dataLayer.push(arguments);}
gtag('js', new Date());
gtag('config', 'G-7SN3NCBBWK');
</script>
<body>
<a href="https://github.com/Nostracodus/earley" class="github-corner" aria-label="View source on GitHub"><svg width="80" height="80" viewBox="0 0 250 250" style="fill:#151513; color:#fff; position: absolute; top: 0; border: 0; right: 0;" aria-hidden="true"><path d="M0,0 L115,115 L130,115 L142,142 L250,250 L250,0 Z"></path><path d="M128.3,109.0 C113.8,99.7 119.0,89.6 119.0,89.6 C122.0,82.7 120.5,78.6 120.5,78.6 C119.2,72.0 123.4,76.3 123.4,76.3 C127.3,80.9 125.5,87.3 125.5,87.3 C122.9,97.6 130.6,101.9 134.4,103.2" fill="currentColor" style="transform-origin: 130px 106px;" class="octo-arm"></path><path d="M115.0,115.0 C114.9,115.1 118.7,116.5 119.8,115.4 L133.7,101.6 C136.9,99.2 139.9,98.4 142.2,98.6 C133.8,88.0 127.5,74.4 143.8,58.0 C148.5,53.4 154.0,51.2 159.7,51.0 C160.3,49.4 163.2,43.6 171.4,40.1 C171.4,40.1 176.1,42.5 178.8,56.2 C183.1,58.6 187.2,61.8 190.9,65.4 C194.5,69.0 197.7,73.2 200.1,77.6 C213.8,80.2 216.3,84.9 216.3,84.9 C212.7,93.1 206.9,96.0 205.4,96.6 C205.1,102.4 203.0,107.8 198.3,112.5 C181.9,128.9 168.3,122.5 157.7,114.1 C157.9,116.9 156.7,120.9 152.7,124.9 L141.0,136.5 C139.8,137.7 141.6,141.9 141.8,141.8 Z" fill="currentColor" class="octo-body"></path></svg></a><style>.github-corner:hover .octo-arm{animation:octocat-wave 560ms ease-in-out}@keyframes octocat-wave{0%,100%{transform:rotate(0)}20%,60%{transform:rotate(-25deg)}40%,80%{transform:rotate(10deg)}}@media (max-width:500px){.github-corner:hover .octo-arm{animation:none}.github-corner .octo-arm{animation:octocat-wave 560ms ease-in-out}}</style>
<div>
<div id="input-pane" class="pane">
<select
id="grammars"
onchange="installGrammar(this)"
style="width: 100%"
class="mb-1 pl-1 pr-1 text-ui"
>
<option>Math</option>
<option>Recursive</option>
<option>Left Recursive</option>
<option>Right Recursive</option>
<option>Hidden Left Recursive</option>
<option>Hidden Right Recursive</option>
<option>PEP</option>
<option>Aho Left</option>
<option>Aho Right</option>
<option>Brackets</option>
<option>EEE</option>
<option>AT aT</option>
<option>ST</option>
<option>aAbB</option>
<option value="Custom">Custom</option>
</select>
<div>
<input
id="input-str"
value="abbb"
class="border pl-1 text-monospace input"
/>
<button
onclick="parseGrammar()"
class="float-r ml-1 text-ui"
style="background-color: #fff"
>
Parse
</button>
</div>
<div class="mt-1">
<div
id="grammar"
contenteditable="true"
class="border text-monospace p-1 input"
></div>
</div>
</div>
<div id="explainer" class="pane text-ui p-2">
<p>
This is a tool that implements the Earley parsing algorithm as given
by Elizabeth Scott and Adrian Johnstone in
<a href="https://core.ac.uk/download/pdf/82746212.pdf"
target="_blank" rel="noopener noreferrer">Recognition is not parsing — SPPF-style parsing from cubic
recognisers</a
>. The input pane has some sample grammars collected from various
parsing papers. Custom grammars and inputs can be supplied in the
forms.
</p>
<p>
Grammars are expected to be in the form
<code>Nonterminal ::= term*</code> with spaces between terms and one
rule per line. Input is expected to be supplied with no spaces. Rules
that can derive the empty string are written with an empty right-hand
side (as in <code>S ::= </code>).
</p>
</div>
<div id="sppf-canvas"></div>
</div>
<script type="text/javascript">
document.getElementById("grammar").addEventListener("input", (_) => {
switchToCustom();
});
let exampleGrammars = {
Custom: {},
Math: {
grammar: [
"E ::= E + T",
"E ::= T",
"T ::= T * F",
"T ::= F",
"F ::= 0",
"F ::= 1",
"F ::= 2",
],
input: "0+1*2",
},
"Left Recursive": {
grammar: ["S ::= S a", "S ::= a"],
input: "aaa",
},
"Right Recursive": {
grammar: ["S ::= a S", "S ::= a"],
input: "aaa",
},
"Hidden Left Recursive": {
grammar: ["S ::= X S a", "S ::= a", "X ::= "],
input: "aaa",
},
"Hidden Right Recursive": {
grammar: ["S ::= a S X", "S ::= a", "X ::= "],
input: "aaa",
},
EEE: {
grammar: ["E ::= E E E", "E ::= 1", "E ::= "],
input: "1",
},
"Aho Right": {
grammar: ["S ::= x S S", "S ::= "],
input: "x",
},
"Aho Left": {
grammar: ["S ::= S S x", "S ::= "],
input: "x",
},
Brackets: {
grammar: ["E ::= E E", "E ::= ( E )", "E ::= "],
input: "()",
},
Recursive: {
grammar: ["S ::= x S x", "S ::= x"],
input: "xxx",
},
"AT aT": {
grammar: [
"S ::= A T",
"S ::= a T",
"A ::= a",
"A ::= B A",
"B ::= ",
"T ::= b b b",
],
input: "abbb",
},
ST: {
grammar: ["S ::= S T", "S ::= a", "B ::= ", "T ::= a B", "T ::= a"],
input: "aa",
},
aAbB: {
grammar: ["S ::= a A b B", "A ::= a", "B ::= A", "B ::= a"],
input: "aaba",
},
"PEP": {
grammar: ["S ::= A A A A", "A ::= E", "A ::= a", "E ::= "],
input: "aa",
},
};
function populateFieldsWithGrammarInfo(grammar) {
let grammarElement = document.getElementById("grammar");
let inputElement = document.getElementById("input-str");
if (grammar.input !== undefined) inputElement.value = grammar.input;
if (grammar.grammar !== undefined)
grammarElement.innerText = grammar.grammar.join("\n");
}
function installGrammar(selectObject) {
return populateFieldsWithGrammarInfo(
exampleGrammars[selectObject.value]
);
}
function switchToCustom() {
let selectObject = document.getElementById("grammars");
selectObject.value = "Custom";
return populateFieldsWithGrammarInfo(exampleGrammars["Custom"]);
}
document.getElementById("grammars").dispatchEvent(new Event("change"));
// Taken from https://stackoverflow.com/questions/58980235/stop-pasting-html-style-in-a-contenteditable-div-only-paste-the-plain-text
// This removes styles when copy-pasting into input selections.
const editable_div = document.getElementById("grammar");
editable_div.addEventListener("paste", function (e) {
e.preventDefault();
const text = e.clipboardData
? (e.originalEvent || e).clipboardData.getData("text/plain")
: window.clipboardData
? window.clipboardData.getData("Text")
: "";
const range = document.getSelection().getRangeAt(0);
range.deleteContents();
const textNode = document.createTextNode(text);
range.insertNode(textNode);
range.selectNodeContents(textNode);
range.collapse(false);
const selection = window.getSelection();
selection.removeAllRanges();
selection.addRange(range);
});
let parseGrammar = () => {
/* As soon as the user parses their input, hide the explainer. They've got the idea
* by now.
*/
let explainerElement = document.getElementById("explainer");
explainerElement.style.visibility = "hidden";
let inputElement = document.getElementById("input-str");
/* In error cases, the input string object will be modified to indicate an error.
* When the user clicks the 'parse' button, we should assume there is no error
* and reset the visual style.
*/
inputElement.classList.remove("error");
inputElement.title = "";
let rawText = document.getElementById("grammar").innerText;
let rules = rawText
.split("\n")
.map((str) => str.trim())
.filter((s) => s.length > 0);
let input = inputElement.value;
const grammar = new Grammar(rules);
const parser = new Parser(grammar, input);
while (!isExhausted(parser) && parser.error === undefined) {
step(parser);
}
if (parser.error !== undefined) {
inputElement.classList.add("error");
inputElement.title = `syntax error at token ${parser.error + 1}`;
} else if (parser.accepted == undefined) {
inputElement.classList.add("error");
inputElement.title = `syntax error: incomplete input`;
} else {
let theme = {
bgcolor: "none",
fgcolor: "#000000",
};
let node = visualization.renderNode(parser.accepted, theme);
var viz = new Viz();
viz
.renderSVGElement(node)
.then((element) => {
let canvas = document.getElementById("sppf-canvas");
canvas.replaceChildren(element);
svgPanZoom("#sppf-canvas > svg");
})
.catch((error) => {
viz = new Viz();
console.error(error);
});
}
};
</script>
</body>
</html>