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Verify Type of a Term |

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- Built-in Predicates
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- Reference manual

Type tests are semi-deterministic predicates that succeed if the
argument satisfies the requested type. Type-test predicates have no
error condition and do not instantiate their argument. See also library
`library(error)`

.

- [ISO]
**var**(`@Term`) - True if
`Term`currently is a free variable. - [ISO]
**nonvar**(`@Term`) - True if
`Term`currently is not a free variable. - [ISO]
**integer**(`@Term`) - True if
`Term`is bound to an integer. - [ISO]
**float**(`@Term`) - True if
`Term`is bound to a floating point number. **rational**(`@Term`)- True if
`Term`is bound to a rational number. Rational numbers include integers. **rational**(`@Term, -Numerator, -Denominator`)- True if
`Term`is a rational number with given`Numerator`and`Denominator`. The`Numerator`and`Denominator`are in canonical form, which means`Denominator`is a positive integer and there are no common divisors between`Numerator`and`Denominator`. - [ISO]
**number**(`@Term`) - True if
`Term`is bound to an integer or floating point number.^{57As rational numbers are not atomic in the current implementation and we do not want to break the rule that number/1 implies atomic/1, number/1 fails on rational numbers. This will change if rational numbers become atomic.} - [ISO]
**atom**(`@Term`) - True if
`Term`is bound to an atom. **blob**(`@Term, ?Type`)- True if
`Term`is a*blob*of type`Type`. See section 12.4.8. **string**(`@Term`)- True if
`Term`is bound to a string. Note that string here refers to the built-in atomic type string as described in section 5.2. Starting with versionĀ 7, the syntax for a string object is text between double quotes, such as`"hello"`

.^{58In traditional Prolog systems, double quoted text is often mapped to a list of character codes.}See also the Prolog flag double_quotes. - [ISO]
**atomic**(`@Term`) - True if
`Term`is bound (i.e., not a variable) and is not compound. Thus, atomic acts as if defined by:atomic(Term) :- nonvar(Term), \+ compound(Term).

SWI-Prolog defines the following atomic datatypes: atom (atom/1), string (string/1), integer (integer/1), floating point number (float/1) and blob (blob/2). In addition, the symbol

`[]`

(empty list) is atomic, but not an atom. See section 5.1. - [ISO]
**compound**(`@Term`) - True if
`Term`is bound to a compound term. See also functor/3 =../2, compound_name_arity/3 and compound_name_arguments/3. - [ISO]
**callable**(`@Term`) - True if
`Term`is bound to an atom or a compound term. This was intended as a type-test for arguments to call/1 and call/2.. Note that callable only tests the*surface term*. Terms such as (22,true) are considered callable, but cause call/1 to raise a type error. Module-qualification of meta-argument (see meta_predicate/1) using

causes callable to succeed on any meta-argument.`:`

/2^{59We think that callable/1 should be deprecated and there should be two new predicates, one performing a test for callable that is minimally module aware and possibly consistent with type-checking in call/1 and a second predicate that tests for atom or compound.}Consider the program and query below::- meta_predicate p(0). p(G) :- callable(G), call(G). ?- p(22). ERROR: Type error: `callable' expected, found `22' ERROR: In: ERROR: [6] p(user:22)

- [ISO]
**ground**(`@Term`) - True if
`Term`holds no free variables. See also nonground/2 and term_variables/2. **cyclic_term**(`@Term`)- True if
`Term`contains cycles, i.e. is an infinite term. See also acyclic_term/1 and section 2.17.^{60The predicates cyclic_term/1 and acyclic_term/1 are compatible with SICStus Prolog. Some Prolog systems supporting cyclic terms use is_cyclic/1 .} - [ISO]
**acyclic_term**(`@Term`) - True if
`Term`does not contain cycles, i.e. can be processed recursively in finite time. See also cyclic_term/1 and section 2.17.

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