Functional Programming
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The document discusses the differences between functional and imperative programming paradigms, highlighting functional programming's focus on immutable data and functions as first-class citizens. It illustrates these concepts with coding examples, emphasizing how functional programming promotes the use of composable, concise functions to build complex systems. The concluded content outlines key rules for avoiding imperative habits in functional programming.
![• A number can be stored in a variable and so can a function:
var fortytwo = function() { return 42 };
• A number can be stored in an array slot and so can a function:
var fortytwos = [42, function() { return 42 }];
• A number can be stored in an object field and so can a function:
var fortytwos = {number: 42, fun: function() { return 42 }};
• A number can be created as needed and so can a function:
42 + (function() { return 42 })(); //=> 84
• A number can be passed to a function and so can a function:
function weirdAdd(n, f) { return n + f() } weirdAdd(42, function() { return 42 });
//=> 84
• A number can be returned from a function and so can a function:
return 42;
return function() { return 42 };](https://image.slidesharecdn.com/functional-150506122241-conversion-gate01/85/Functional-Programming-11-320.jpg)
![Imperative
var lyrics = [];
for (var bottles = 99; bottles > 0; bottles--) {
lyrics.push(bottles + " bottles of beer on the wall”);
lyrics.push(bottles + " bottles of beer");
lyrics.push("Take one down, pass it around");
if (bottles > 1) {
lyrics.push((bottles - 1) + " bottles of beer on the wall.");
} else {
lyrics.push("No more bottles of beer on the wall!”);
}
}](https://image.slidesharecdn.com/functional-150506122241-conversion-gate01/85/Functional-Programming-18-320.jpg)
![functional
function lyricSegment(n) {
return _.chain([])
.push(n + " bottles of beer on the wall")
.push(n + " bottles of beer”)
.push("Take one down, pass it around")
.tap(function(lyrics) {
if (n > 1)
lyrics.push((n - 1) + " bottles of beer on the wall.");
else
lyrics.push("No more bottles of beer on the wall!");
})
.value();
}](https://image.slidesharecdn.com/functional-150506122241-conversion-gate01/85/Functional-Programming-19-320.jpg)
![functional
lyricSegment(9);
//=> ["9 bottles of beer on the wall",
// "9 bottles of beer",
// "Take one down, pass it around",
// "8 bottles of beer on the wall."]](https://image.slidesharecdn.com/functional-150506122241-conversion-gate01/85/Functional-Programming-20-320.jpg)
![functional
function song(start, end, lyricGen) {
return _.reduce(_.range(start,end,-1),
function(acc,n) {
return acc.concat(lyricGen(n));
}, []);
}
And using it is as simple as:
song(99, 0, lyricSegment);
//=> ["99 bottles of beer on the wall",
// ...
// "No more bottles of beer on the wall!"]](https://image.slidesharecdn.com/functional-150506122241-conversion-gate01/85/Functional-Programming-21-320.jpg)
Functional Programming
- 3. modifying mutable variables using assignments and control structures such as if, then, else, lops, break, continue, return
- 5. modifying mutable variables assignments programming without and other imperative control structures
- 6. programming focusing on the functions functions ARE values that can be produced, consumed and composed
- 8. Immutable Data Functional programs should be immutable, which means you would simply create new data structures instead of modifying ones that already exist.
- 9. Referential transparency Functional programs should perform every task as if for the first time, with no knowledge of what may or may not have happened earlier in the program’s execution and without side effects.
- 10. Function as first-class citizens functions can be defined anywhere they can be passed as parameters to functions and returned as results there exists a set of operators to compose functions
- 11. • A number can be stored in a variable and so can a function: var fortytwo = function() { return 42 }; • A number can be stored in an array slot and so can a function: var fortytwos = [42, function() { return 42 }]; • A number can be stored in an object field and so can a function: var fortytwos = {number: 42, fun: function() { return 42 }}; • A number can be created as needed and so can a function: 42 + (function() { return 42 })(); //=> 84 • A number can be passed to a function and so can a function: function weirdAdd(n, f) { return n + f() } weirdAdd(42, function() { return 42 }); //=> 84 • A number can be returned from a function and so can a function: return 42; return function() { return 42 };
- 12. Composing Functions In functional programming, you’re always looking for simple, repeatable actions to be abstracted out into a function. We can then build more complex features by calling these functions in sequence
- 13. "Functional programming is the use of functions that transform values into units of abstraction, subsequently used to build software systems."
- 14. code examples Give a 10% discount to all products of the chart above $30 Show the total value of products and discount
- 15. Imperative Double valorTotal = 0d; Double descontoTotal = 0d; for (Produto produto : produtos) { valorTotal += produto.getValor(); if (produto.getValor() > 30.00) { descontoTotal += produto.getValor() * 0.1; } } valorTotal -= descontoTotal;
- 16. functional val valores = produtos map (_.valor) val valorTotal = valores reduce ((total, valor) => total + valor) val descontoTotal = valores filter (_ > 30.00) map (_ * 0.10) reduce ((total, desconto) => total + desconto) val total = valorTotal - descontoTotal
- 17. code examples Write a program to build a lyric sheet for the song “99 bottles of beer" X bottles of beer on the wall X bottles of beer Take one down, pass it around X-1 bottles of beer on the wall No more bottles of beer on the wall
- 18. Imperative var lyrics = []; for (var bottles = 99; bottles > 0; bottles--) { lyrics.push(bottles + " bottles of beer on the wall”); lyrics.push(bottles + " bottles of beer"); lyrics.push("Take one down, pass it around"); if (bottles > 1) { lyrics.push((bottles - 1) + " bottles of beer on the wall."); } else { lyrics.push("No more bottles of beer on the wall!”); } }
- 19. functional function lyricSegment(n) { return _.chain([]) .push(n + " bottles of beer on the wall") .push(n + " bottles of beer”) .push("Take one down, pass it around") .tap(function(lyrics) { if (n > 1) lyrics.push((n - 1) + " bottles of beer on the wall."); else lyrics.push("No more bottles of beer on the wall!"); }) .value(); }
- 20. functional lyricSegment(9); //=> ["9 bottles of beer on the wall", // "9 bottles of beer", // "Take one down, pass it around", // "8 bottles of beer on the wall."]
- 21. functional function song(start, end, lyricGen) { return _.reduce(_.range(start,end,-1), function(acc,n) { return acc.concat(lyricGen(n)); }, []); } And using it is as simple as: song(99, 0, lyricSegment); //=> ["99 bottles of beer on the wall", // ... // "No more bottles of beer on the wall!"]
- 22. 1. All of your functions must accept at least one argument. 2. All of your functions must return data or another function. 3. No loops 3 simple rules to avoid imperative habits
- 23. conclusions data abstractions composing functions declarative programming concise code
- 24. Coursera: Functional Programming Principles in Scala Book: Functional Javascript, Michael Fogus http://www.smashingmagazine.com/2014/07/02/dont-be-scared-of-functional- programming/ References