Subsections

- Exercises

# Abbreviated declarations

You have now met many identity declarations. When declaring names, it is apparent that much of the declaration is repeated on both sides. For example:

       REF[]REAL r = LOC[10]REAL

Declarations of names are very common in Algol 68 programs and abbreviated declarations are available. The above declaration can be written

       LOC[10]REAL r

or, most commonly

       [10]REAL r

An abbreviated declaration uses the actual-declarer (the right-hand side of an identity declaration) followed by the identifier; and if the actual-declarer contains the generator `LOC`, you can omit the `LOC` (see section 6.1 which explains actual-declarers and formal-declarers).

Here are some of the declarations given as examples in this chapter rewritten in their abbreviated form:

       INT a;
       REAL x:=pi;
       CHAR s;
       [7]INT i7;
       [0:6]INT i7 at 0;
       [3]INT k:=(1,2,3);
       [3,3]REAL x; [0:2,0:2]REAL y;
       FLEX[1:0]INT fn;
       [36]CHAR sf;
       [(INT i; read(i); i)]INT r

It is important to note that identity declarations should not be mixed with abbreviated name declarations because the modes are quite different. For example, in

       REAL a:=2.4;
       REAL b = a+2.1

the mode of `a` is `REF REAL`, but the mode of `b` is `REAL`. In the abbreviated declaration of a name, the mode given is that of the value to which the name will refer (the actual-declarer).

When you declare a new object, if you do not intend assigning to it, use an identity declaration. Only declare it as a name if you intend superseding the value to which it will refer. Remember that assignment can be dangerous because values are superseded.

## Exercises

5.19
  Write abbreviated declarations for the following:
  Ans
  (a)
    `REF[]CHAR rc = LOC[1000]CHAR`

  (b)
    `REF FLEX[]INT fi = LOC FLEX[1:0]INT`

  (c)
    `REF BOOL b = LOC BOOL := TRUE`

5.20
  Write full identity declarations for the following:
  Ans
  (a)
    `INT a,b,c`

  (b)
    `REAL x;[5]CHAR y;[3,3]REAL z`

  (c)
    `FLEX[1:0]CHAR s`