What is a predicate in Lisp?

What is a predicate in Lisp?

Advertisements. Predicates are functions that test their arguments for some specific conditions and returns nil if the condition is false, or some non-nil value is the condition is true.

Is nil an atom in Lisp?

The symbol nil is an atom and is also a list; it is the only Lisp object that is both. This function returns t if object is a cons cell or nil .

How do you not equal a Lisp?

/= (not Equal to) (AutoLISP) Note that the behavior of /= does not quite conform to other LISP dialects. The standard behavior is to return T if no two arguments in the list have the same value. In AutoLISP, /= returns T if no successive arguments have the same value; see the examples that follow.

What does Eq do in Lisp?

Lisp’s equality operators are: = compares only numbers, regardless of type. eq compares symbols. Two objects are eq iff they are actually the same object in memory.

What is a predicate condition?

A predicate is a condition expression that evaluates to a boolean value, either true or false. Predicates can be used as follows: In a SELECT statement’s WHERE clause or HAVING clause to determine which rows are relevant to a particular query. Note that not all predicates can be used in a HAVING clause.

What is predicate logic example?

Example − “Man is mortal” can be transformed into the propositional form ∀xP(x) where P(x) is the predicate which denotes x is mortal and the universe of discourse is all men.

What does cons mean in Lisp?

In computer programming, cons (/ˈkɒnz/ or /ˈkɒns/) is a fundamental function in most dialects of the Lisp programming language. cons constructs memory objects which hold two values or pointers to two values. These objects are referred to as (cons) cells, conses, non-atomic s-expressions (“NATSes”), or (cons) pairs.

How do you say not equal in Scheme?

The not operation always returns #t or #f. Since Scheme doesn’t have a numeric “not equals” operator (like the != operator in C/Java/Python), we have to combine not and = in order to evaluate “not equals”. The Scheme interpreter runs in a Read-Evaluate-Print Loop (REPL).

How do you compare two numbers in a lisp?

Compatibility note: In Common Lisp, the comparison operations perform “mixed-mode” comparisons: (= 3 3.0) is true. In MacLisp, there must be exactly two arguments, and they must be either both fixnums or both floating-point numbers. To compare two numbers for numerical equality and type equality, use eql.

What is SETQ in Lisp?

(setq var1 form1 var2 form2 …) is the simple variable assignment statement of Lisp. First form1 is evaluated and the result is stored in the variable var1, then form2 is evaluated and the result stored in var2, and so forth. setq may be used for assignment of both lexical and dynamic variables.

What is Mapcar Lisp?

mapcar is a function that calls its first argument with each element of its second argument, in turn. The second argument must be a sequence.

What is a false predicate?

False predicates are actually a logic problem; the subject doesn’t fit logically with the predicate. Ex: Financial aid is a problem. (Financial aid is the subject and is a problem is the predicate. But logically, financial aid is NOT a problem.

How do you negate predicate logic?

To negate a sequence of nested quantifiers, you flip each quantifier in the sequence and then negate the predicate. So the negation of ∀x ∃y : P(x, y) is ∃x ∀y : P(x, y) and So the negation of ∃x ∀y : P(x, y) and ∀x ∃y : P(x, y).

What is cons and nil?

Conses are a data type, and nil is the sole object of type null. The Lisp data type list is taken to mean the union of the cons and null data types, and therefore encompasses both true lists and dotted lists.

What is Terpri in Lisp?

Frill-free printing in LISP is achieved with print, prin1, princ and terpri. The simplest uses of print, prin1, and princ involve a single argument. Terpri, which produces a newline, can be called with no arguments. All these are functions.

What is null in Scheme?

In Scheme, there is one null pointer value, called “the empty list,” which prints as () . (Later, we’ll see why it’s written that way, and why it’s called “the empty list.”) Conceptually, the empty list is a special object, and a “null” pointer is a pointer to this special end-of-list object.

What is CDR and car in Scheme?

In Scheme, car , cdr , and cons are the most important functions. The cons function is used to construct pairs and pairs are used to construct the lists. The car and cdr are used to access data and return accordingly first and second element from a pair.

How do you compare two strings in Lisp?

[Function] string= compares two strings and is true if they are the same (corresponding characters are identical) but is false if they are not.