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書名： Professional Scala
作者名： Mads Hartmann Ruslan Shevchenko
本章字數： 314字
更新時間： 2021-07-23 17:24:23

Base Syntax for Expressions

Scala is an expression-based language, which means that everything is an expression (in the right-hand side of function and value/variable definitions).

Some of the base expressions are:

Primitive expression: Constant or value/variable name.
Function calls: These can be:
- Usual function calls f(x, y).
- Operator call syntax:
- binary: x + y.
Note

Any method with an argument can be used as a binary operator. A set of predefined binary operators are similar to Java:
unary: !x
Constructors: new x creates an instance of class x.
Assignments to mutable variables:
- y = 3: Assigns a value of 3 to y.
- x = 3: This is a compiler error, and a value can't be assigned.
Block:
```
{ A; B }
```
The value of a block expression is the last expression. Note that ; can be omitted if A and B are situated on different lines. The syntax for this is shown as follows:
```
{
   A
   B
}
```

The preceding syntax will have the same output as { A; B }.

Control structures

if statement:

       >  if (1 == 1)  "A"  else "B"
       - let's eval one in REPL

match/case expressions:

    >  x match {
         case "Jon"  =>  doSomethingSpecialForJon()
         case "Joe" =>   doSomethingSpecialForJoe()
         case   _   => doForAll()
      }

Loops:

while/do

     var i=0
      var s=0
      while(i < 10) {
          s = s+i
          i = i +1
      }

Do/while
Foreach, for

Shortcuts for height-order functions will be described in detail in, Chapter 4, Scala Collections.

We'll look at defining a main function which prints something onscreen and calls the main function.

You should have already opened project1. If you haven't, import it into the IDE.
Insert the new method inside the object definition.
Insert call at the main method.

The full method should look something like this:

  object Chatbot1 {def printHello():Unit = {
println("Hello")}def main(args: Array[String]): Unit = {
printHello() … // unchanged code here
     }
}

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Professional Scala

Base Syntax for Expressions

Note