February 17, 2009

The development of FORTRAN. A story of innovation. The 25th Anniversary of FORTRAN video.

TEST on Thursday.

Test will be multiple choice and essay questions.

Sample questions

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SCOPE

When a language allows different variables to have the same name, it must have some way to ensure that each use of the name is unambiguous. This means there must be some way to control the scope of definitions.

fun square n = n * n;

fun twotmes n = n + n;

	int main () {
    int n = 3;
    int m;
    m = n + 5;
    printf m;
    {
        int n = 6;
        m = n + 4;
        printf m;
    }
    printf m;
}

A definition is anything that establishes a possible binding for a name.

fun cube x = x * x *x ;

fun cube cube = cube * cube * cube;

def cube( cube):

return cube * cube * cube;

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Static scope - definitions determined at compile time

Dynamic scope - definitions determined at run time.

1      program main;
2      var x: integer;
3      procedure Q(var i:integer; function R(j:integer):integer);
4              var x: integer;
5              begin
6                      x := 4;
7                      writeln('before call to R', i,x);
8                      i := R(i);
9                      writeln('after call to R',i,x);
10             end;
11     procedure P;
12             var i : integer;
13             function FN(k : integer):integer;
14                     begin
15                             x := x + k;
16                             FN := i + k;
17                             writeln('in FN',i,x);
18                     end;
19             begin
20                     i := 2;
21                     Q(x,FN);
22                     writeln('in P', i, x);
23             end;
24     begin
25             x :=  7;
26             p;
27             writeln('in main',x);
28     end.

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Scoping with labeled namespaces

A labeled namespace is any language construct that contains definitions and a region of the program where those definitions apply, and also has a name that can be used to access those definitions from the outside.

IN ML

structure Fred = struct

val a = 1;

fun f x = x + a;

end;

outside can access Fred.a or Fred.f

class in java or C++ is another example. There we can mark items as public or private

This work is licensed under a Creative Commons License.
Ernest Ackermann Department of Computer Science, Mary Washington College
CPSC 110 | CPSC 330 | CPSC 401

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SCOPE

Static scope - definitions determined at compile time Dynamic scope - definitions determined at run time.

Scoping with labeled namespaces

Static scope - definitions determined at compile time

Dynamic scope - definitions determined at run time.