Merge branch 'master' of https://github.com/dmitriz/functional-examples

Author: dmitriz

README.md

@@ -1,17 +1,26 @@
-# functional-examples
-Examples with Functional JavaScript
+### functional-examples
+
+
+
+
+
+## [New functional library `cpsfy`](https://github.com/dmitriz/cpsfy)
+
+UPDATE. Check out my new advanced functional library: 
+https://github.com/dmitriz/cpsfy
+
+# Examples with Functional JavaScript
 
 Heavily annotated examples from the awesome videos
 <a href="https://egghead.io/lessons/javascript-refactoring-imperative-code-to-a-single-composed-expression-using-box">Professor Frisby Introduces Composable Functional JavaScript</a>,
 see also <a href="https://www.reddit.com/r/javascript/comments/5hfq6n/100_minutes_of_free_functional_programming/">the discussion on Reddit</a> and <a href="https://news.ycombinator.com/item?id=13167149">on Hacker News</a>.
 
 See also the wonderful e-book <a href="https://drboolean.gitbooks.io/mostly-adequate-guide/content/">
 Professor Frisby's Mostly Adequate Guide to Functional Programming</a>
-by the same author.
+by the same author (See also https://github.com/MostlyAdequate/mostly-adequate-guide for the updates).
 
 
 ## What makes Prof. Frisby's course and book awesome?
-
 Both course and book amazingly manage to avoid suffering from the two widespread diseases when explaining abstract functional concepts: 
 
 - The first disease is to stay with abstract artifically simplified examples that can be easily manipulated 
@@ -29,7 +38,6 @@ demonstrating real benefits of the functional abstractions with sharp focus and
 
 
 ## Running Examples
-
 Install the packages with either of
 ```js
 yarn install
@@ -42,5 +50,4 @@ node <file.js>
 
 
 ## Related Projects
-
 - [Monadic Libraries Examples with Tests](https://github.com/dmitriz/monadic-libraries-examples)

examples/01-box.js renamed to examples/01-identity-functor-box.js

@@ -11,7 +11,8 @@ const Box = x => (
     // so we can keep chaining
     map: f => Box(f(x)),
 
-    // fold functor map, applies f and returns the raw unwrapped value,
+    // not part of the functor spec
+    // applies f and returns the raw unwrapped value,
     // sends f:a->b into fold(f):Box(a)->b,
     // does not return any Box container, so can't be chained with map
     fold: f => f(x),
@@ -35,13 +36,13 @@ const nextCharForNumberString = str =>
 
 const result = nextCharForNumberString(' 64 ')
 
-console.log('nextCharForNumberString for 64 is: ', result) //=> a
+console.log(`console.log displays nextCharForNumberString('64') as: `, result)
 
 
 
 // ==== Experiments
 
-console.log(Box(22))
+console.log(`Box(22) is displayed as: `, Box(22))
 
 const inspectBox = x => (
   {
@@ -53,4 +54,4 @@ const inspectBox = x => (
   }
 )
 
-console.log(inspectBox(4)) //=> I am wrapping '4'
+console.log(`Custom inspect shows 'inspectBox(4)' as: `, inspectBox(4)) //=> I am wrapping '4'

examples/02-refactor.js renamed to examples/02-identity-double-wrap.js

@@ -10,24 +10,25 @@ const Box = x => (
     // so we can keep chaining
     map: f => Box(f(x)),
 
-    // fold functor map, applies f and returns the raw unwrapped value,
+    // not part of functor spec
+    // applies f and returns the raw unwrapped value,
     // sends f:a->b into fold(f):Box(a)->b,
     // does not return any Box container, so can't be chained with map
     fold: f => f(x),
 
     // custom getter function -- called by console.log
-    inspect: () => `Box(${x})`
+    inspect: () => x.inspect ? `Box(${x.inspect()})` : `Box(${x})`
   }
 )
 
-
+// String => Box(String)
 const moneyToFloat =  str =>
   Box(str)
     .map(s => s.replace(/\$/g, ''))
     .map(r => parseFloat(r))
     // .fold(r => parseFloat(r))
 
-
+// String => Box(String)
 const percentToFloat = str =>
   Box(str.replace(/\%/g, ''))
     .map(replaced => parseFloat(replaced))
@@ -59,10 +60,26 @@ const applyDiscount = (price, discount) =>
     )
 
 
-console.log(moneyToFloat(' $33 ')) //=> Box(33)
-console.log(percentToFloat(' 1.23% ')) //=> Box(0.0123)
+// without fold, result is wrapped into Box twice
+const applyDiscountInBox = (price, discount) =>
+  moneyToFloat(price).map(cost =>
+
+    // nesting so cost remains in scope
+    percentToFloat(discount).map(savings =>
+      cost - cost * savings
+    )
+  )
+
+
+console.log(`moneyToFloat(' $33 ') : `, moneyToFloat(' $33 ')) //=> Box(33)
+console.log(`percentToFloat(' 1.23% ') : `, percentToFloat(' 1.23% ')) //=> Box(0.0123)
 
 const result = applyDiscount('$55', '20%')
 
-console.log(result) //=> 44
+console.log(`applyDiscount('$55', '20%') : `, result) //=> 44
+
+console.log(
+  `applyDiscountInBox('$55', '20%') : `, 
+  applyDiscountInBox('$55', '20%')
+) //=> Box(Box(44))
 

examples/03-right-left.js

@@ -15,7 +15,7 @@ const Right = x => (
 const Left = x => (
   {
 
-    // Left ignores f, simply passes x itself
+    // Left ignores f, simply passes ahead raw value x
     map: f => Left(x),
 
     // applies the function on the left and returns raw value
@@ -37,8 +37,8 @@ const resultLeft = Left(3)
   .map(x => x + 1)
   .map(x => x / 2)
 
-console.log(resultRight) //=> Right(2)
-console.log(resultLeft) //=> Left(3)
+console.log(`Right(3) transformed: `, resultRight) //=> Right(2)
+console.log(`Left(3) transformed: `,resultLeft) //=> Left(3)
 
 
 // passing Right value,
@@ -51,6 +51,8 @@ const result = Right(2)
   // left function handles error, right function returns the value
   .fold(x => 'error', x => x)
 
+console.log(`Right(2) transformed and unwrapped with (x => 'error', x => x): `, result) //=> 1.5
+
 
 // passing Left value,
 // so all functions are ignored
@@ -62,9 +64,7 @@ const resultError = Left(2)
   // left function handles error, right function returns the value
   .fold(x => 'error', x => x)
 
-console.log(result) //=> 1.5
-console.log(resultError) //=> error
-
+console.log(`Left(2) transformed and unwrapped with (x => 'error', x => x): `, resultError) //=> error
 
 
 const findColor = name =>
@@ -78,15 +78,18 @@ const resultColor = findColor('red')
   .slice(1)
   .toUpperCase()
 
-console.log(resultColor)
+console.log(`findColor('red') transformed is: `, resultColor)
 
 
-const findColorFixed = name => {
+const findColorCases = name => {
   const found = {red: '#ff4444', blue: '#00ff00'}[name]
   return found ? Right(found) : Left(null)
 }
 
-const badColor = findColorFixed('gray')
+console.log(`findColorCases('gray') is: `, findColorCases('gray')) //=> no color
+
+
+const badColor = findColorCases('gray')
 
   // map only applies when passed Right,
   // ignored when passed Left
@@ -96,21 +99,21 @@ const badColor = findColorFixed('gray')
     c => c.toUpperCase()
   )
 
-console.log(badColor) //=> no color
+console.log(`findColorCases('gray') transformed and fold with (e => 'no color', c => c.toUpperCase()) is: `, badColor) //=> no color
 
 
 
-// ensure null will always go Left
+// ensure null (of any falsey value) will always go to Left
 const fromNullable = x =>
   x != null ? Right(x) : Left(null)
 
 // no need anymore to worry about null in our logic
 // much simpler function, no more cases
-const findColorNew = name =>
+const findColorFromNullable = name =>
   fromNullable({red: '#ff4444', blue: '#00ff00'}[name])
 
 
-const badColorNew = findColorNew('gray')
+const badColorNew = findColorFromNullable('gray')
 
   // map only applies when passed Right,
   // ignored when passed Left
@@ -120,5 +123,8 @@ const badColorNew = findColorNew('gray')
     c => c.toUpperCase()
   )
 
-console.log(badColorNew) //=> no color
+console.log(
+  `findColorFromNullable('gray') transformed and fold with (e => 'no color', c => c.toUpperCase()) is: `, 
+  badColorNew
+) //=> no color
 

examples/04-fs-error-handling.js

@@ -51,7 +51,7 @@ const getPort = fileName =>
 
   // this will not "explode" if fileName is not found!
   tryCatch( () => fs.readFileSync(fileName) )
-    .map(c => JSON.parse(c))
+    .map( c => JSON.parse(c) )
 
     // .map(c => tryCatch(() => JSON.parse(c)))
     .fold(
@@ -61,25 +61,30 @@ const getPort = fileName =>
       c => c.port
     )
 
-console.log(getPort()) //=> 3000
-console.log(getPort('con.json')) //=> 3000
-console.log(getPort('config.json')) //=> 8080
+// no file passed
+console.log(`getPort() : `, getPort()) //=> 3000
 
+// file not present
+console.log(`getPort('con.json') : `, getPort('con.json')) //=> 3000
 
+// file present
+console.log(`getPort('config.json') : `, getPort('config.json')) //=> 8080
 
-const getPortNew = fileName =>
-  tryCatch(() => fs.readFileSync(fileName))
-  .chain(c => tryCatch(() => JSON.parse(c)))
+
+
+// protecting against further errors by wrapping into tryCatch
+const getPortSafe = fileName =>
+  tryCatch( () => fs.readFileSync(fileName) )
+  .chain( c => tryCatch(() => JSON.parse(c)) )
   .fold(
     e => 3000,
     c => c.port
   )
 
 
-console.log(getPortNew()) //=> 3000
-console.log(getPortNew('con.json')) //=> 3000
+console.log(`getPortSafe() : `, getPortSafe()) //=> 3000
+console.log(`getPortSafe('con.json') : `, getPortSafe('con.json')) //=> 3000
 
 // importing badly formatted file
-console.log(getPortNew('configBad.json')) //=> 3000
-console.log(getPort('config.json')) //=> 8080
-
+console.log(`getPortSafe('configBad.json') : `, getPortSafe('configBad.json')) //=> 3000
+console.log(`getPortSafe('config.json') : `, getPortSafe('config.json')) //=> 8080