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CSCI 305: Programming Languages

Scope Part I

Reading: Webster Ch. 10

Instructions

1. Watch This Video - (11:21)
2. Watch This Video - (15:02)
3. Watch This Video - (16:47)
4. Review the Lecture Slides
5. Complete the Out of Class Exercise
6. Check your learning
7. Attend Class and complete the In Class Exercises
8. Check your learning

Out of Class Exercise

Here is the example used to show primitive namespaces in Java:

class Reuse {
    Reuse Reuse(Reuse Reuse) {
        Reuse:
           for (;;) {
               if (Reuse.Reuse(Reuse) == Reuse)
                  break Reuse;
           }
           return Reuse;
    }
}

Copy it and then annotate it as follows:

• For each occurrence of the name Reuse that is a definition, describe what binding for Reuse is established
• For each occurrence of Reuse that is not a definition, show which definition is used to bind it.

Check Your Learning:

Solution:

Definition	Binding
class Reuse	Binding for the type Reuse
method Reuse()	Binding for the method Reuse of type Reuse -> Reuse
parameter Reuse	Binding for the parameter Reuse of type Reuse in the Method Reuse
label Reuse:	Binding for the labeled block Reuse

Use of Reuse	Binding Used
Reuse.Reuse	bound to the method Reuse in the Class Reuse
(Reuse)	bound to the parameter Reuse of the method Reuse in the class Reuse
== Reuse	bound to the parameter Reuse of the method Reuse in the class Reuse
break Reuse	bound to the Label Reuse
return Reuse	bound to the parameter Reuse of the method Reuse in the class Reuse

In Class Exercises

Exercise

Here is the example used to show the difference between scoping with blocks and dynamic scoping:

fun g x =
   let
      val inc = 1;
      fun f y = y + inc;
      fun h z =
        let
          val inc = 2;
        in
          f z
        end;
   in
      h x
   end;

Copy it and then annotate it as follows:

• Draw a circle around every block, and number the blocks.
• Identify each definition of a name.
• For each definition, describe its scope in terms of your block numbers
• For each occurrence of a name (other than a definition of that name), show which definition is used to bind it. Check that this agrees with your scopes.

Check Your Learning:

Solution:

/--------------------------------------------------------------------------\
|            /---------------------------------------------------------\ 0 |
|      fun g | x =                                                   1 |   |
| /----------/                                                         |   |
| |   /-------------------------------------------------------------\  |   |
| |   |   let                                                     2 |  |   |
| |   |      val inc = 1;                                           |  |   |
| |   |            /---------------------\                          |  |   |
| |   |      fun f | y = y + inc;      3 |                          |  |   |
| |   |            \---------------------/                          |  |   |
| |   |            /---------------------------------------------\  |  |   |
| |   |      fun h | z =                                       4 |  |  |   |
| |   | /----------/                                             |  |  |   |
| |   | |  /-------------------------------------------------\   |  |  |   |
| |   | |  |   let                                         5 |   |  |  |   |
| |   | |  |     val inc = 2;                                |   |  |  |   |
| |   | |  |   in                                            |   |  |  |   |
| |   | |  |     f z                                         |   |  |  |   |
| |   | |  |   end;                                          |   |  |  |   |
| |   | |  \-------------------------------------------------/   |  |  |   |
| |   | \--------------------------------------------------------/  |  |   |
| |   |   in                                                        |  |   |
| |   |      h x                                                    |  |   |
| |   |   end;                                                      |  |   |
| |   \-------------------------------------------------------------/  |   |
| \--------------------------------------------------------------------/   |
\--------------------------------------------------------------------------/

Definition	Scope		Name	Binding
g	{0,1,2,3,4,5}		y in y + inc	y:{3}
x	{1,2,3,4}		inc in y + inc	inc:{2,3,4}
inc	{2,3,4}		f in f z	f:{2,3,4,5}
f	{2,3,4,5}		z in f z	z:{4,5}
y	{3}		h in h x	h:{2,3,4,5}
h	{2,4,5,3}		x in h x	x:{1,2,3,4}
z	{4,5}
inc	{5}