Java methods do not accept methods as arguments

(unlike, say, rex)

There are two ways of getting the effect of a function such as map:

• Code a map specifically for the function being applied, i.e. "wire-in" the function
  
• Simulate a function as an argument using an object

The second of these requires some ideas more advanced than we can present right now, so we illustrate only the first.

Wired-in version of map:

In order to achieve a map effect, refer to a possible definition of map in rex:

map(F, [ ]) => [ ];

map(F, [A | L]) => [F(A) | map(F, L)];

In Java, suppose the function is a known static method. Only the list is an argument:

static IntList mapF(IntList L)

{

if( isEmpty(L) )

  return IntList.nil;

 

return IntList.cons(F(IntList.first(L)), mapF(IntList.rest(L)));

}

 

For example, if we wanted to square each element of a list, then F would be defined as:

static int F(int x)

{

return x*x;

}