OpenMusic 6 – User ManualHierarchie de section : Advanced Visual Programming > Control Structures > Predicates > Equality PredicatesEquality Predicates
In Lisp, equality can be interpreted different ways. For instance, the character "a" is a concept that can be represented by several different glyphs – A, a, a – which can be considered identical or not, depending on the predicate. These predicates are not available in the menus : their name must be typed directly in a patch editor.
Functionalities
There are four equality test predicates :
- eq
- eql
- equal
- equalp.
The eq and eql predicates are the strictest, the equal and equalp are the most open predicates, and are relevant to most cases.
|
Returns "t" with |
Examples | |
|---|---|---|
|
|
identical objects with the same reference integers and ratios of same value glyphs representing the same character -> "nil" : strings, lists, floats, ratios that produce floats. |
eq A A -> t eq 2 2/1 -> t eq A a -> t eq "A" "A" -> nil eq (A B C) (A B C) -> nil eq 2.5 2.5 -> nil |
|
Returns "t" with |
Examples | |
|
|
eq or eql objects structurally similar objects strings with identical glyphs floats of same value |
equal (A (b) C) (a (B) c) -> t equal "A" "A" -> t equal "A" "a" ->nil equal 2.5 2.5 ->t |
|
Returns "t" with |
Examples | |
|
|
eq, eql or equal objects strings with similar glyphs numbers of same numerical value |
equalp "A" "a" -> t equalp 2 2/1 -> t equalp 2.5 2.5 -> t equalp 2 2.0 -> t |
- For instance, two chords with the same reference are eq.
- In some cases, equal considers the object. In other cases, equal considers the concept.
- Equalp only considers values and concepts, not their representation.
Equality Predicates in Lisp and OM Functions
Many Lisp and OM functions need a predicate to operate.
Functions that perform operations upon lists, for instance, have a default equality predicate used for identifying similar items in two different lists, and manipulate them. Note that this predicate can be redefined to modify the behaviour of the function.
