Order indicators

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Order indicators

$\begin{verbsyntax}\onerule{OrderIndicator}{'first' \vert 'last' \vert 'next' \vert 'prev' \vert 'before' \vert 'after' \vert 'any'} \end{verbsyntax}$

If users specify predicates that refer to fields of list-functor type, special order indicators can be used to find out certain special elements of the list. The order indicators generate an access to specific list elements. There are the following types, exemplified by a relation Stmts, the statements of a block:

Stmts[first](Block,S1) generates an access to the first element S1 in the Stmts of Block.
Stmts[last](Block,S1) generates an access to the last element S1 in the Stmts of Block.
Stmts[any](Block,S1) generates an access to an arbitrary element S1 in the Stmts of Block. For lists the head of the list is taken. This indicator can also be applied to set functors. Then it emits a call to the choose-function of the set functor.
Stmts[after in Block](S1,S2) generates a loop over all successors S2 of S1 in the Stmts of Block.
Stmts[before in Block](S1,S2) generates a loop over all predecessors S2 of S1 in the Stmts of Block.
Stmts[next in Block](S1,S2) generates an access to the successor S2 of S1 in the Stmts of Block.
Stmts[prev in Block](S1,S2) generates an access to the predecessor S2 of S1 in the Stmts of Block.

The variable Block must be defined earlier in the specification.

The distribution contains a demo file autotest/examples/test-list-add.ox for order indicators.

Next: All-quantified predicates Up: Predicates in rules Previous: Relation modifiers

Uwe Assmann
1998-12-22