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A huge re-organization of the Scala file

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Geoff Liu
2014-11-10 19:24:00 -07:00
parent 459967e446
commit 57c9f70417
1 changed files with 295 additions and 267 deletions
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scala.html.markdown
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@@ -4,6 +4,7 @@ filename: learnscala.scala
contributors: contributors:
- ["George Petrov", "http://github.com/petrovg"] - ["George Petrov", "http://github.com/petrovg"]
- ["Dominic Bou-Samra", "http://dbousamra.github.com"] - ["Dominic Bou-Samra", "http://dbousamra.github.com"]
- ["Geoff Liu", "http://geoffliu.me"]
filename: learn.scala filename: learn.scala
--- ---
@@ -20,16 +21,16 @@ Scala - the scalable language
scala> scala>
This is the so called REPL. You can run commands in the REPL. Let's do just This is the so called REPL (Read-Eval-Print Loop). You may type any valid
that: Scala expression into it, and the result will be printed. We will explain what
Scala files look like further into this tutorial, but for now, let's start
with some basics.
*/ */
println(10) // prints the integer 10
println("Boo!") // printlns the string Boo! #################################################
## 1. Basics
#################################################
// Some basics
// Printing, and forcing a new line on the next print // Printing, and forcing a new line on the next print
println("Hello world!") println("Hello world!")
@@ -82,9 +83,50 @@ true == false // false
*/ */
// Everything is an object, including a function. Type these in the REPL: // Strings
7 // results in res30: Int = 7 (res30 is just a generated var name for the result) "Scala strings are surrounded by double quotes" //
'a' // A Scala Char
'Single quote strings don't exist' // Error
"Strings have the usual Java methods defined on them".length
"They also have some extra Scala methods.".reverse
// Seealso: scala.collection.immutable.StringOps
println("ABCDEF".length)
println("ABCDEF".substring(2, 6))
println("ABCDEF".replace("C", "3"))
// String interpolation
val n = 45
println(s"We have $n apples") // => "We have 45 apples"
// Expressions inside interpolated strings are also possible
val a = Array(11, 9, 6)
println(s"My second daughter is ${a(0) - a(2)} years old.") // => "My second daughter is 5 years old."
println(s"We have double the amount of ${n / 2.0} in apples.") // => "We have double the amount of 22.5 in apples."
println(s"Power of 2: ${math.pow(2, 2)}") // => "Power of 2: 4"
// Formatting with interpolated strings (note the prefixed f)
println(f"Power of 5: ${math.pow(5, 2)}%1.0f") // "Power of 5: 25"
println(f"Square root of 122: ${math.sqrt(122)}%1.4f") // "Square root of 122"
// Ignoring special characters.
println(raw"New line feed: \n. Carriage return: \r.") // => "New line feed: \n. Carriage return: \r."
// Some characters need to be 'escaped', e.g. a double quote inside a string:
val a = "They stood outside the \"Rose and Crown\"" // => "They stood outside the "Rose and Crown""
// Triple double-quotes let strings span multiple rows and contain quotes
val html = """<form id="daform">
<p>Press belo', Joe</p>
| <input type="submit">
</form>"""
#################################################
## 2. Functions
#################################################
// The next line gives you a function that takes an Int and returns it squared // The next line gives you a function that takes an Int and returns it squared
(x:Int) => x * x (x:Int) => x * x
@@ -108,25 +150,67 @@ sq(10) // Gives you this: res33: Int = 100.
// taking an Int and returning an Int. // taking an Int and returning an Int.
val add10: Int => Int = _ + 10 val add10: Int => Int = _ + 10
// Scala allows methods and functions to return, or take as parameters, other
// functions or methods.
List(1, 2, 3) map add10 // List(11, 12, 13) - add10 is applied to each element #################################################
## 3. Flow Control
#################################################
// Anonymous functions can be used instead of named functions: 1 to 5
List(1, 2, 3) map (x => x + 10) val r = 1 to 5
r.foreach( println )
// And the underscore symbol, can be used if there is just one argument to the r foreach println
// anonymous function. It gets bound as the variable // NB: Scala is quite lenient when it comes to dots and brackets - study the
List(1, 2, 3) map (_ + 10) // rules separately. This helps write DSLs and APIs that read like English
// If the anonymous block AND the function you are applying both take one (5 to 1 by -1) foreach ( println )
// argument, you can even omit the underscore
List("Dom", "Bob", "Natalia") foreach println // A while loops
var i = 0
while (i < 10) { println("i " + i); i+=1 }
while (i < 10) { println("i " + i); i+=1 } // Yes, again. What happened? Why?
i // Show the value of i. Note that while is a loop in the classical sense -
// it executes sequentially while changing the loop variable. while is very
// fast, faster that Java // loops, but using the combinators and
// comprehensions above is easier to understand and parallelize
// A do while loop
do {
println("x is still less than 10");
x += 1
} while (x < 10)
// Tail recursion is an idiomatic way of doing recurring things in Scala.
// Recursive functions need an explicit return type, the compiler can't infer it.
// Here it's Unit.
def showNumbersInRange(a:Int, b:Int):Unit = {
print(a)
if (a < b)
showNumbersInRange(a + 1, b)
}
// Conditionals
// Data structures val x = 10
if (x == 1) println("yeah")
if (x == 10) println("yeah")
if (x == 11) println("yeah")
if (x == 11) println ("yeah") else println("nay")
println(if (x == 10) "yeah" else "nope")
val text = if (x == 10) "yeah" else "nope"
var i = 0
while (i < 10) { println("i " + i); i+=1 }
#################################################
## 4. Data Structures
#################################################
val a = Array(1, 2, 3, 5, 8, 13) val a = Array(1, 2, 3, 5, 8, 13)
a(0) a(0)
@@ -175,109 +259,25 @@ d._1
d._2 d._2
#################################################
## 5. Object Oriented Programming
#################################################
// Combinators /*
Aside: Everything we've done so far in this tutorial has been simple
expressions (values, functions, etc). These expressions are fine to type into
the command-line interpreter for quick tests, but they cannot exist by
themselves in a Scala file. For example, you cannot have just "val x = 5" in
a Scala file. Instead, the only top-level constructs allowed in Scala are:
s.map(sq) - objects
- classes
- case classes
- traits
val sSquared = s. map(sq) And now we will explain what these are.
*/
sSquared.filter(_ < 10)
sSquared.reduce (_+_)
// The filter function takes a predicate (a function from A -> Boolean) and
// selects all elements which satisfy the predicate
List(1, 2, 3) filter (_ > 2) // List(3)
List(
Person(name = "Dom", age = 23),
Person(name = "Bob", age = 30)
).filter(_.age > 25) // List(Person("Bob", 30))
// Scala a foreach method defined on certain collections that takes a type
// returning Unit (a void method)
aListOfNumbers foreach (x => println(x))
aListOfNumbers foreach println
// For comprehensions
for { n <- s } yield sq(n)
val nSquared2 = for { n <- s } yield sq(n)
for { n <- nSquared2 if n < 10 } yield n
for { n <- s; nSquared = n * n if nSquared < 10} yield nSquared
/* NB Those were not for loops. The semantics of a for loop is 'repeat', whereas
a for-comprehension defines a relationship between two sets of data. */
// Loops and iteration
1 to 5
val r = 1 to 5
r.foreach( println )
r foreach println
// NB: Scala is quite lenient when it comes to dots and brackets - study the
// rules separately. This helps write DSLs and APIs that read like English
(5 to 1 by -1) foreach ( println )
// A while loops
var i = 0
while (i < 10) { println("i " + i); i+=1 }
while (i < 10) { println("i " + i); i+=1 } // Yes, again. What happened? Why?
i // Show the value of i. Note that while is a loop in the classical sense -
// it executes sequentially while changing the loop variable. while is very
// fast, faster that Java // loops, but using the combinators and
// comprehensions above is easier to understand and parallelize
// A do while loop
do {
println("x is still less than 10");
x += 1
} while (x < 10)
// Tail recursion is an idiomatic way of doing recurring things in Scala.
// Recursive functions need an explicit return type, the compiler can't infer it.
// Here it's Unit.
def showNumbersInRange(a:Int, b:Int):Unit = {
print(a)
if (a < b)
showNumbersInRange(a + 1, b)
}
// Conditionals
val x = 10
if (x == 1) println("yeah")
if (x == 10) println("yeah")
if (x == 11) println("yeah")
if (x == 11) println ("yeah") else println("nay")
println(if (x == 10) "yeah" else "nope")
val text = if (x == 10) "yeah" else "nope"
var i = 0
while (i < 10) { println("i " + i); i+=1 }
// Object oriented features
// Classname is Dog
class Dog { class Dog {
//A method called bark, returning a String //A method called bark, returning a String
def bark: String = { def bark: String = {
@@ -289,8 +289,6 @@ class Dog {
// Classes can contain nearly any other construct, including other classes, // Classes can contain nearly any other construct, including other classes,
// functions, methods, objects, case classes, traits etc. // functions, methods, objects, case classes, traits etc.
// Case classes // Case classes
case class Person(name:String, phoneNumber:String) case class Person(name:String, phoneNumber:String)
@@ -298,8 +296,12 @@ case class Person(name:String, phoneNumber:String)
Person("George", "1234") == Person("Kate", "1236") Person("George", "1234") == Person("Kate", "1236")
// Objects and traits coming soon!
// Pattern matching
#################################################
## 6. Pattern Matching
#################################################
val me = Person("George", "1234") val me = Person("George", "1234")
@@ -338,49 +340,75 @@ matcher("52917") // => "No match on '52917'"
matcher("52752-16432-22178-47917") // => "Serial key: 52752, 16432, 22178, 47917" matcher("52752-16432-22178-47917") // => "Serial key: 52752, 16432, 22178, 47917"
// Strings #################################################
## 7. Functional Programming
#################################################
"Scala strings are surrounded by double quotes" // // Scala allows methods and functions to return, or take as parameters, other
'a' // A Scala Char // functions or methods.
'Single quote strings don't exist' // Error
"Strings have the usual Java methods defined on them".length
"They also have some extra Scala methods.".reverse
// Seealso: scala.collection.immutable.StringOps List(1, 2, 3) map add10 // List(11, 12, 13) - add10 is applied to each element
println("ABCDEF".length) // Anonymous functions can be used instead of named functions:
println("ABCDEF".substring(2, 6)) List(1, 2, 3) map (x => x + 10)
println("ABCDEF".replace("C", "3"))
// String interpolation // And the underscore symbol, can be used if there is just one argument to the
val n = 45 // anonymous function. It gets bound as the variable
println(s"We have $n apples") // => "We have 45 apples" List(1, 2, 3) map (_ + 10)
// Expressions inside interpolated strings are also possible // If the anonymous block AND the function you are applying both take one
val a = Array(11, 9, 6) // argument, you can even omit the underscore
println(s"My second daughter is ${a(0) - a(2)} years old.") // => "My second daughter is 5 years old." List("Dom", "Bob", "Natalia") foreach println
println(s"We have double the amount of ${n / 2.0} in apples.") // => "We have double the amount of 22.5 in apples."
println(s"Power of 2: ${math.pow(2, 2)}") // => "Power of 2: 4"
// Formatting with interpolated strings (note the prefixed f)
println(f"Power of 5: ${math.pow(5, 2)}%1.0f") // "Power of 5: 25"
println(f"Square root of 122: ${math.sqrt(122)}%1.4f") // "Square root of 122"
// Ignoring special characters.
println(raw"New line feed: \n. Carriage return: \r.") // => "New line feed: \n. Carriage return: \r."
// Some characters need to be 'escaped', e.g. a double quote inside a string:
val a = "They stood outside the \"Rose and Crown\"" // => "They stood outside the "Rose and Crown""
// Triple double-quotes let strings span multiple rows and contain quotes
val html = """<form id="daform">
<p>Press belo', Joe</p>
| <input type="submit">
</form>"""
// Combinators
// Application structure and organization s.map(sq)
val sSquared = s. map(sq)
sSquared.filter(_ < 10)
sSquared.reduce (_+_)
// The filter function takes a predicate (a function from A -> Boolean) and
// selects all elements which satisfy the predicate
List(1, 2, 3) filter (_ > 2) // List(3)
List(
Person(name = "Dom", age = 23),
Person(name = "Bob", age = 30)
).filter(_.age > 25) // List(Person("Bob", 30))
// Scala a foreach method defined on certain collections that takes a type
// returning Unit (a void method)
aListOfNumbers foreach (x => println(x))
aListOfNumbers foreach println
// For comprehensions
for { n <- s } yield sq(n)
val nSquared2 = for { n <- s } yield sq(n)
for { n <- nSquared2 if n < 10 } yield n
for { n <- s; nSquared = n * n if nSquared < 10} yield nSquared
/* NB Those were not for loops. The semantics of a for loop is 'repeat', whereas
a for-comprehension defines a relationship between two sets of data. */
#################################################
## 8. Implicits
#################################################
Coming soon!
#################################################
## 9. Misc
#################################################
// Importing things // Importing things
import scala.collection.immutable.List import scala.collection.immutable.List