The FORALL loop
Keywords: pame

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The `FORALL` loop

The `FORALL` loop is not part of Algol 68, but an extension introduced by the a68toc compiler. It is similar to the `FOR` loop, but the identifier has the mode of an element of the multiple under consideration. Look at this example:

       []REAL r1 = (1.0,2.0,3.0,4.0,5.0);
       FORALL e IN r1 DO print(e * e) OD

In the `FORALL` loop, `e` takes the value of each element in `r1` and so has mode `REAL`. The compiler generates more efficient code using the `FORALL` loop by avoiding the normal overheads of the subscripting mechanism. However, the `FORALL` loop can only be used when all the elements of a dimension are required. If you want to limit the processing to a few elements, you can trim the multiple or use the `FOR` loop.

The elements of more than one multiple can be combined simultaneously. For example:

       []INT i = (1,2,3,4,5),
             j = (11,12,13,14,15);
       FORALL ii IN i, jj IN j
       DO
          print((ii * jj,newline))
       OD

The comma between `ii IN i` and `jj IN j` means that the constructs are elaborated collaterally. The bounds of `i` must be the same as the bounds of `j`.

`FORALL` clauses can be nested as in the case of `FOR` clauses. If we use `l` and `m` declared in a previous example, then

       FORALL ll IN l
       DO
          FORALL mm IN m
          DO
             print(ll * mm)
          OD
       OD

could be used to print the products of all the integers.