Concepts of Programming Languages

Scala Pragmatics

Get Java and Scala

Unzip the Scala homework workspace from
here (if you use Programming in Scala 4th edition)
or here (if you use Programming in Scala 5th edition)
Follow the instructions in README.html
Install Java LTS (long term support) v8 or v11
or OpenJDK/AdoptOpenJDK (e.g., via homebrew) v8 or v11
Install SBT using the windows installer or homebrew.

Using Scala

For real programs and homeworks, use sbt to run tests

file may only contain object and class declarations


object o { val x = ... }
class c { ... }

You can use console/:quit to get a REPL within sbt

In the sbt REPL, you can use import objects


// Scala 3                        
import o.*
// use x


// Scala 2
import o._
// use x

Using scala

For tiny examples, type directly into the REPL
```
val x = ... 
// use x
              
```

Using scala

For larger examples, type in a file and paste into the REPL
```
// Scala 3                    
:load x.sc
// use x
                  
```
```
// Scala 2                    
:paste x.sc
// use x
                  
```
- File contains declarations just as you would type them in the REPL
- If there are expressions, then the last one is printed out as a value in the REPL.
- If you use the file ending .scala, then do not put the file x.scala in the SBT directory. If you do, then SBT will try to compile it and give you an error, since SBT requires files to contain only object and class declarations.
- I use the file ending .sc for snippet files.

Disassembly (Scala2 only)

To see what scala is doing, you can disassemble in the REPL


scala> class C { val x:Int = 1}
defined class C

scala> :javap -p -c -filter C
Compiled from "<console>"
public class C {
  private final int x;

  public int x();
    Code:
       0: aload_0
       1: getfield      #18                 // Field x:I
       4: ireturn

  public C();
    Code:
       0: aload_0
       1: invokespecial #24                 // Method java/lang/Object."<init>":()V
       4: aload_0
       5: iconst_1
       6: putfield      #18                 // Field x:I
       9: return
}

Disassembly (Scala2 only)

You can also see the previous REPL declaration


scala> def x = 1
x: Int

scala> :javap -p -c -filter -
Compiled from "<console>"
public class  {
  public static  MODULE$;

  public static {};
    Code:
       0: new           #2                  // class 
       3: invokespecial #17                 // Method "<init>":()V
       6: return

  public int x();
    Code:
       0: iconst_1
       1: ireturn

  public ();
    Code:
       0: aload_0
       1: invokespecial #21                 // Method java/lang/Object."<init>":()V
       4: aload_0
       5: putstatic     #23                 // Field MODULE$:L;
       8: return
}

Homework

testOnly fp1tests
testOnly fp1tests -- -n fp1ex05
~testOnly fp1tests