** Next:** Examples of the
**Up:** The FORALL Construct
** Previous:** General Form of

Execution of a `FORALL` construct consists of the following steps:

- Evaluation in any order of the
*subscript*and*stride*expressions in the*forall-triplet-spec-list*. The set of*valid combinations*of*index-name*values is then the Cartesian product of the sets defined by these triplets. - Evaluation of the
*scalar-mask-expr*for all valid combinations of*index-name*values. The mask elements may be evaluated in any order. The set of*active combinations*of*index-name*values is the subset of the valid combinations for which the mask evaluates to`.TRUE.` - Execute the
*forall-body-stmts*in the order they appear. Each statement is executed completely (that is, for all active combinations of*index-name*values) according to the following interpretation:- Statements in the
*forall-assignment*category (i.e. assignment statements and pointer assignment statements) evaluate the*expr*and all expressions within*variable*(in the case of*assignment-stmt*) or*target*and all expressions within*pointer-object*(in the case of*pointer-assignment-stmt*) of the*forall-assignment*for all active combinations of*index-name*values. These evaluations may be done in any order. The*expr*values are then assigned to the corresponding*variable*locations (in the case of*assignment-stmt*) or the*target*values are associated with the corresponding*pointer-object*locations (in the case of*pointer-assignment-stmt*). The assignment or association operations may also be performed in any order. - Statements in the
*where-stmt*and*where-construct*categories evaluate their*mask-expr*for all active combinations of values of*index-name*s. All elements of all masks may be evaluated in any order. The`WHERE`statement's assignment (or assignments within the`WHERE`branch of the construct) are then executed in order using the above interpretation of array assignments within the`FORALL`, but the only array elements assigned are those selected by both the active*index-name*values and the`WHERE`mask. Finally, the assignments in the`ELSEWHERE`branch are executed if that branch is present. The assignments here are also treated as array assignments, but elements are only assigned if they are selected by both the active combinations and by the negation of the`WHERE`mask. - Statements in the
*forall-stmt*and*forall-construct*categories first evaluate the*subscript*and*stride*expressions in the*forall-triplet-spec-list*for all active combinations of the outer`FORALL`constructs. The set of valid combinations of*index-names*for the inner`FORALL`is then the union of the sets defined by these bounds and strides for each active combination of the outer*index-names*, the outer*index names*being included in the combinations generated for the inner`FORALL`. The scalar mask expression is then evaluated for all valid combinations of the inner`FORALL`'s*index-names*to produce the set of active combinations. If there is no scalar mask expression, it is as if it were present with the constant value`.TRUE.`Each statement in the inner`FORALL`is then executed for each active combination (of the inner`FORALL`), recursively following the interpretations given in this section.

- Statements in the

If the scalar mask expression is omitted, it is as if it were
present with the value `.TRUE.`

The scope of an *index-name* is the `FORALL` construct itself.

Each *forall-assignment* must obey the same restrictions in a
*forall-construct* as in a simple *forall-stmt*. In
addition, each *where-stmt* or assignment nested within a *where-construct* must obey these restrictions. (Note that any
innermost statement within nested `FORALL` constructs must fall
into one of these two categories.) For example, an assignment may not
cause the same array element to be assigned more than once. Different
statements may, however, assign to the same array element, and
assignments made in one statement may affect the execution of a later
statement.

Thu Jul 21 17:05:43 CDT 1994