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OM 6.5 – User ManualVisual Programming II > Control Structures > Predicates > In Practice
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Predicates: In Practice

Predicates can be used as conditions defining the execution of an operation. Hence, predicates must be connected to

  • the "test" input of an OMIF box,

  • to a function that has a test argument .

If a given property or a relation is verified by a predicate, the operation is performed.

Example : Using a Type Predicate as a Test Argument

Here, we want to delete floats from a list with list-filter. List-filter rejects or passes elements from a list, depending on the predicate taken as argument.

It has three default inputs :

  1. a predicate, whose default value is numberp

  2. a list

  3. an action – "reject" or "pass".

The floatp predicate and the "reject" option have been assigned to list-filter, so that floats are rejected.

  • List-filter tests each element of the list successively.
  • If the test is satisfied, the element is either rejected, or passed, depending on the option that was chosen.
  • The remaining elements are returned in a list.
Using a Function on Lambda Mode

A predicate can be a function on "lambda" mode.

Using a Lambda Function as a Predicate
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