100 lines
3.3 KiB
Markdown
100 lines
3.3 KiB
Markdown
---
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title: S-Expressions
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id: 59667989bf71cf555dd5d2ff
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challengeType: 5
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forumTopicId: 302303
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---
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## Description
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<section id='description'>
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<a href="https://en.wikipedia.org/wiki/S-Expression" title="wp: S-Expression" target="_blank">S-Expressions</a> are one convenient way to parse and store data.
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</section>
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## Instructions
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<section id='instructions'>
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Write a simple reader/parser for S-Expressions that handles quoted and unquoted strings, integers and floats.
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The function should read a single but nested S-Expression from a string and return it as a (nested) array.
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Newlines and other whitespace may be ignored unless contained within a quoted string.
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"<tt>()</tt>" inside quoted strings are not interpreted, but treated as part of the string.
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Handling escaped quotes inside a string is optional; thus "<tt>(foo"bar)</tt>" may be treated as a string "<tt>foo"bar</tt>", or as an error.
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For this, the reader need not recognize "<tt>\</tt>" for escaping, but should, in addition, recognize numbers if the language has appropriate data types.
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Note that with the exception of "<tt>()"</tt>" ("<tt>\</tt>" if escaping is supported) and whitespace there are no special characters. Anything else is allowed without quotes.
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The reader should be able to read the following input
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<pre>
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((data "quoted data" 123 4.5)
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(data (!@# (4.5) "(more" "data)")))
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</pre>
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and turn it into a native data structure. (See the <a href="https://rosettacode.org/wiki/S-Expressions#Pike" title="#Pike" target="_blank">Pike</a>, <a href="https://rosettacode.org/wiki/S-Expressions#Python" title="#Python" target="_blank">Python</a> and <a href="https://rosettacode.org/wiki/S-Expressions#Ruby" title="#Ruby" target="_blank">Ruby</a> implementations for examples of native data structures.)
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</section>
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## Tests
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<section id='tests'>
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```yml
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tests:
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- text: <code>parseSexpr</code> is a function.
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testString: assert(typeof parseSexpr === 'function');
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- text: <code>parseSexpr('(data1 data2 data3)')</code> should return <code>['data1', 'data2', 'data3']</code>
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testString: assert.deepEqual(parseSexpr(simpleSExpr), simpleSolution);
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- text: <code>parseSexpr('(data1 data2 data3)')</code> should return an array with 3 elements.
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testString: assert.deepEqual(parseSexpr(basicSExpr), basicSolution);
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```
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</section>
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## Challenge Seed
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<section id='challengeSeed'>
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<div id='js-seed'>
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```js
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function parseSexpr(str) {
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// Good luck!
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return true;
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}
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```
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</div>
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### After Test
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<div id='js-teardown'>
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```js
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const simpleSExpr = '(data1 data2 data3)';
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const simpleSolution = ['data1', 'data2', 'data3'];
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const basicSExpr = '((data "quoted data" 123 4.5) (data (!@# (4.5) "(more" "data)")))';
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const basicSolution = [["data","\"quoted data\"",123,4.5],["data",["!@#",[4.5],"\"(more\"","\"data)\""]]];
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```
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</div>
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</section>
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## Solution
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<section id='solution'>
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```js
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function parseSexpr(str) {
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const t = str.match(/\s*("[^"]*"|\(|\)|"|[^\s()"]+)/g);
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for (var o, c = 0, i = t.length - 1; i >= 0; i--) {
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var n,
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ti = t[i].trim();
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if (ti == '"') return;
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else if (ti == '(') t[i] = '[', c += 1;
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else if (ti == ')') t[i] = ']', c -= 1;
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else if ((n = +ti) == ti) t[i] = n;
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else t[i] = `'${ti.replace('\'', '\\\'')}'`;
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if (i > 0 && ti != ']' && t[i - 1].trim() != '(') t.splice(i, 0, ',');
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if (!c) if (!o) o = true; else return;
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}
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return c ? undefined : eval(t.join(''));
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}
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```
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</section>
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