24:null 25:["$","title",null,{"children":"Exercise: Closures & Currying | Anjana Vakil | Observable"}] 2a:T51e,grumpyQuotes = html`${[ quote( 'Guido van Rossum', 2001, "Don't you hate code that's not properly indented?" ), // https://slashdot.org/story/01/04/20/1455252/guido-van-rossum-unleashed quote( 'Doug Crockford', 2005, 'There are no good texts on JavaScript programming.' ), // http://crockford.com/javascript/style1.html quote( 'Doug Crockford', 2008, 'JavaScript is an astonishing language, in the very worst sense.' ), // http://crockford.com/javascript/popular.html quote( 'Edsger Dijkstra', 1978, 'Object oriented programming is an exceptionally bad idea which could only have originated in California.' ), // https://www.quora.com/Why-did-Dijkstra-say-that-%E2%80%9CObject-oriented-programming-is-an-exceptionally-bad-idea-which-could-only-have-originated-in-California-%E2%80%9D/answer/Terry-Moore-32 quote( 'Edsger Dijkstra', 1975, 'By claiming that they can contribute to software engineering, the soft scientists make themselves even more ridiculous.' ), // https://www.cs.utexas.edu/users/EWD/ewd04xx/EWD498.PDF quote( 'Edsger Dijkstra', 1975, "Besides a mathematical inclination, an exceptionally good mastery of one's native tongue is the most vital asset of a competent programmer." ) // ibid. ]}`2b:[] 28:{"id":"d00db6d5662fa62c","slug":"exercise-closures-currying","title":"Exercise: Closures & Currying","thumbnail":"9ae2827ba3ffccc314a48ada7e82688d484513902489b376306d26d8f71b3abd","access_level":"public","create_time":"$D2020-12-03T04:58:42.798Z","update_time":"$D2020-12-05T19:10:35.175Z","view_time":null,"first_public_time":"$D2020-12-04T16:18:33.656Z","has_unpublished_edits":null,"fork":false,"stars":5,"starred":false,"owner":{"type":"team","id":"8cc6a24956698638","login":"anjana","name":"Anjana Vakil","avatar_url":"https://avatars-next.observableusercontent.com/75f0346d6c6908da9b546556f8d223eceb871857b81263c0d62ed549cc492936","tier":"starter_2024"},"version":238,"publish_version":238,"role":null,"authored":false,"authors":[{"type":"individual","id":"d7d614fa2258860d","login":"anjana","name":"Anjana Vakil","avatar_url":"https://avatars-next.observableusercontent.com/75f0346d6c6908da9b546556f8d223eceb871857b81263c0d62ed549cc492936","tier":null}],"members":[{"type":"individual","id":"d7d614fa2258860d","login":"anjana","name":"Anjana Vakil","avatar_url":"https://avatars-next.observableusercontent.com/75f0346d6c6908da9b546556f8d223eceb871857b81263c0d62ed549cc492936","tier":null,"role":"editor"}],"comments":[],"custom_thumbnail":true,"trashed":false,"lapsed":null,"subscribed":null,"forks":186,"collection":{"id":"6c39527ae997d025","slug":"functional-javascript-first-steps","title":"Functional JavaScript First Steps","owner":{"id":"8cc6a24956698638","login":"anjana","name":"Anjana Vakil"}},"type":"notebook","body":{"title":"Exercise: Closures & Currying","cells":[{"id":104,"value":"md`# Exercise: Closures & Currying\n\nWhen a function is defined within another function, the inner function can remember things about the outer function's scope at the time it (the inner function) was defined. This \"remembering\", aka closure, is useful for avoiding long function signatures in the stateless functional world where we need to pass in all relevant inputs as arguments.\n`","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":9,"value":"md`## Exercise: Basic closures\n\n\nThe \\`writeMessage\\` function below takes a message, a salutation (e.g. \"Farewell\" or \"Best regards\"), and a name, and formats them into a signed message like one might use in an email:\n`","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":19,"value":"function writeMessage(message, salutation, name) {\n return md`

${message}

${salutation},
${name}

`;\n}","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":22,"value":"writeMessage(\n \"You're doing amazing! Hopefully these exercises help you get a bit _closure_ to your programming goals.\",\n \"Keep _currying_ on\",\n \"Functional Pungrammer\"\n)","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":81,"value":"md`We can can create a \"pre-signed\" message writer using a function \\`signMessageFrom\\` which takes in a name, and returns a closure - a new function that takes in only a message and salutation and passes them, along with the \"remembered\" name, to the full \\`writeMessage\\` function:`","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":54,"value":"function signMessageFrom(name) {\n return (message, salutation) => writeMessage(message, salutation, name);\n}","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":61,"value":"writeFriendlyNote = signMessageFrom(\"Your best bud\")","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":75,"value":"writeFriendlyNote(\"Hey pal! Party at my place tonight, bring snacks!\", \"See ya\")","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":14,"value":"md`**Fill in the TODOs** in the cells below to complete the \\`signMessageWith\\` and \\`makeSignature\\` functions, which should also return closures. Once the functions are completed, you should see the appropriate messages appear.`","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":44,"value":"function signMessageWith(salutation) {\n return () => {} // TODO replace this function\n}","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":45,"value":"writeBusinessMemo = signMessageWith('Best')","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":48,"value":"writeBusinessMemo(\"Hi, Peter. We need to talk about your TPS reports.\", \"Bob\")","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":65,"value":"function makeSignature(salutation, name) {\n return () => {}; // TODO replace this function\n}","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":66,"value":"writeLoveLetter = makeSignature(\"Thine evermore\", \"William\")","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":70,"value":"writeLoveLetter(\n \"Shall I compare thee to a summer's day? Thou art more lovely and more temperate.\"\n)","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":108,"value":"md`----\n\n## Exercise: Currying`","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":127,"value":"md`\nTo make functions more modular and easier to reuse, we can use techniques like currying, which lets us take advantage of closure to turn a function with any number of arguments into a series of single-argument functions, such that we can provide only some of the input arguments and get a \"partially applied\" function.\n`\n\n","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":130,"value":"md`Below we define the \\`quote\\` function to attribute a (grumpy) statement to a given (grumpy) person and year:`","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":145,"value":"function quote(name, year, text) {\n return md`

\"${text}\"
- ${name} (${year})

`;\n}","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":133,"value":"md`**Check out the function's usage & output** in the cell below.
**Have a good laugh** at how grumpy all these programmers were/are.`","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":143,"value":"$2a","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":136,"value":"md`Unfortunately, even though several quotes share the same author or both author & year, due to the signature of \\`quote\\` we had to re-type all 3 values every time. We couldn't reuse anything.\n\n**Fill in the \\`curriedQuote\\` function below** to \"curry\" the original \\`quote\\` function into reusable, single-argument functions that save us from having to repeat ourselves so much. Look at the cells below to understand what shape the function should take. \n\nOnce \\`curriedQuote\\` is properly implemented, the red error messages below should disappear and the output of \\`stillGrumpyQuotes\\` should be exactly the same as the original \\`grumpyQuotes\\`.\n`","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":183,"value":"curriedQuote = () => {} // TODO replace this placeholder function","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":196,"value":"quoteCrockford = curriedQuote('Doug Crockford')","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":195,"value":"quoteDijkstra = curriedQuote('Edsger Dijkstra')","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":199,"value":"quoteDijkstra75 = quoteDijkstra(1975)","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":181,"value":"stillGrumpyQuotes = html`${[\n curriedQuote('Guido van Rossum')(2001)(\n \"Don't you hate code that's not properly indented?\"\n ),\n\n quoteCrockford(2005)('There are no good texts on JavaScript programming.'),\n\n quoteCrockford(2008)(\n 'JavaScript is an astonishing language, in the very worst sense.'\n ),\n\n quoteDijkstra(1978)(\n 'Object oriented programming is an exceptionally bad idea which could only have originated in California.'\n ),\n\n quoteDijkstra75(\n 'By claiming that they can contribute to software engineering, the soft scientists make themselves even more ridiculous.'\n ),\n\n quoteDijkstra75(\n \"Besides a mathematical inclination, an exceptionally good mastery of one's native tongue is the most vital asset of a competent programmer.\"\n ),\n\n quoteDijkstra75(\n \"The irony of my self-contradiction is lost on me. [Just kidding, he didn't actually say this one - making it all the more true!]\"\n )\n]}`","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":236,"value":"md`-----\n\n## [=> Solutions](https://observablehq.com/@anjana/solutions-closures-currying)\n\n_Just one possible way to solve this exercise, not the only way!_\n`","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":233,"value":"md`----\n\n_And now, a word from our sponsors..._\n\n## The Lambda Calculus\n\n\n`","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"}],"files":"$W2b","stdlib":"1","titling":"auto"}} 29:"$28:body"