- Reference manual
- Built-in Predicates
- Notation of Predicate Descriptions
- Character representation
- Loading Prolog source files
- Editor Interface
- Verify Type of a Term
- Comparison and Unification of Terms
- Control Predicates
- Meta-Call Predicates
- Delimited continuations
- Exception handling
- Printing messages
- Handling signals
- DCG Grammar rules
- Declaring predicate properties
- Examining the program
- Input and output
- Status of streams
- Primitive character I/O
- Term reading and writing
- Analysing and Constructing Terms
- Analysing and Constructing Atoms
- Localization (locale) support
- Character properties
- Character Conversion
- Misc arithmetic support predicates
- Built-in list operations
- Finding all Solutions to a Goal
- Formatted Write
- Global variables
- Terminal Control
- Operating System Interaction
- File System Interaction
- User Top-level Manipulation
- Creating a Protocol of the User Interaction
- Debugging and Tracing Programs
- Debugging and declaring determinism
- Obtaining Runtime Statistics
- Execution profiling
- Memory Management
- Windows DDE interface
- Built-in Predicates
- Reference manual
4.5 Verify Type of a Term
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
- True if Term currently is a free variable.
- True if Term currently is not a free variable.
- True if Term is bound to an integer.
- True if Term is bound to a floating point number.
- 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.
- True if Term is bound to a rational number (including integers) or a floating point number.
- True if Term is bound to an atom.
- blob(@Term, ?Type)
- True if Term is a blob of type Type. See section 12.4.9.
- 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 version 7, the syntax for a string object is
text between double quotes, such as
"hello".63In traditional Prolog systems, double quoted text is often mapped to a list of character codes. See also the Prolog flag double_quotes.
- 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.
- True if Term is bound to a compound term. See also functor/3 =../2, compound_name_arity/3 and compound_name_arguments/3.
- True if Term is bound to an atom or a compound term. This was
intended as a type-test for arguments to call/1, call/2
etc. 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)
causes callable to succeed on any meta-argument.64We 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:  p(user:22)
- True if Term holds no free variables. See also nonground/2 and term_variables/2.
- True if Term contains cycles, i.e. is an infinite term. See also acyclic_term/1 and section 2.17.65The predicates cyclic_term/1 and acyclic_term/1 are compatible with SICStus Prolog. Some Prolog systems supporting cyclic terms use is_cyclic/1 .
- 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.