121 lines
3.3 KiB
Markdown
121 lines
3.3 KiB
Markdown
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---
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title: S-Expressions
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id: 59667989bf71cf555dd5d2ff
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challengeType: 5
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---
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## Description
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<section id='description'>
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<p>
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<a href="https://en.wikipedia.org/wiki/S-Expression" title="wp: S-Expression">S-Expressions</a> are one convenient way to parse and store data.
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</p>
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Task:
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<p>
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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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</p>
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<p>
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The function should read a single but nested S-Expression from a string and
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return it as a (nested) array.
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</p>
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<p>
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Newlines and other whitespace may be ignored unless contained within a quoted string.
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</p>
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<p>“<tt>()</tt>” inside quoted strings are not interpreted, but treated as part of the string.
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</p>
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<p>
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Handling escaped quotes inside a string is optional; thus “<tt>(foo"bar)</tt>” maybe treated as a string “<tt>foo"bar</tt>”, or as an error.
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</p>
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<p>
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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 datatypes.
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</p>
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<p>
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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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</p>
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<p>The reader should be able to read the following input</p>
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<p>
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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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</p>
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<p>
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and turn it into a native datastructure. (see the
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<a href="http://rosettacode.org/wiki/#Pike" title="#Pike">Pike</a>,
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<a href="http://rosettacode.org/wiki/#Python" title="#Python">Python</a> and
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<a href="http://rosettacode.org/wiki/#Ruby" title="#Ruby">Ruby</a> implementations
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for examples of native data structures.)
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</p>
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</section>
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## Instructions
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<section id='instructions'>
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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'', ''<code>parseSexpr</code> is a function.'');'
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- text: '<code>parseSexpr(''(data1 data2 data3)'')</code> should return [''data1'', ''data2'', ''data3'']")'
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testString: 'assert.deepEqual(parseSexpr(simpleSExpr), simpleSolution, "<code>parseSexpr(''(data1 data2 data3)'')</code> should return [''data1'', ''data2'', ''data3'']");'
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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, "<code>parseSexpr(''(data1 data2 data3)'')</code> should return an array with 3 elements");'
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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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console.info('after the test');
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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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