These predicates convert between Prolog constants and lists of ASCII
values. The predicates atom_codes/2, number_codes/2
behave the same when converting from a constant to a list of ASCII
values. When converting the other way around, atom_codes/2
will generate an atom,
will generate a number or exception and name/2
will return a number if possible and an atom otherwise.
The ISO standard defines atom_chars/2
to describe the `broken-up' atom as a list of one-character atoms
instead of a list of codes. Upto version 3.2.x, SWI-Prolog's atom_chars/2
behaved, compatible to Quintus and SICStus Prolog, like atom_codes. As
of 3.3.x SWI-Prolog
are compliant to the ISO standard.
To ease the pain of all variations in the Prolog community, all
SWI-Prolog predicates behave as flexible as possible. This implies the
`list-side' accepts either a code-list or a char-list and the
`atom-side' accept all atomic types (atom, number and string).
Convert between an atom and a list of ASCII values. If Atom
is instantiated, if will be translated into a list of ASCII values and
the result is unified with String. If Atom is
unbound and String is a list of ASCII values, it will Atom
will be unified with an atom constructed from this list.
but CharList is a list of one-character atoms rather than a
list of ASCII values (15).
?- atom_chars(hello, X).
X = [h, e, l, l, o]
- char_code(?Atom, ?ASCII)
Convert between character and ASCII value for a single character. (16)
Similar to atom_chars/2,
but converts between a number and its representation as a list of
one-character atoms. Fails with a
representation_error if Number is unbound and
CharList does not describe a number.
but converts to a list of character codes (normally ASCII values) rather
than one-character atoms. In the mode -, +, both predicates behave
identically to improve handling of non-ISO source.
- name(?AtomOrInt, ?String)
String is a list of ASCII values describing Atom.
Each of the arguments may be a variable, but not both. When String
is bound to an ASCII value list describing an integer and Atom
is a variable Atom will be unified with the integer value
described by String (e.g. `
name(N, "300"), 400 is N +
Convert Int to an ASCII representation
using base Base and unify the result with Atom. If Base
<> 10 the base will be prepended to Atom. Base
= 0 will try to interpret
Int as an ASCII value and return
Otherwise 2 =<Base =< 36. Some examples are
|int_to_atom(45, 2, A)||--> ||A
= 2'101101 |
|int_to_atom(97, 0, A)||--> ||A
= 0'a |
|int_to_atom(56, 10, A)||--> ||A
= 56 |
int_to_atom(Int, 10, Atom).
Succeeds if Atom describes a term that unifies with Term.
Atom is instantiated Atom is converted and then
Term. If Atom has no valid syntax, a
exception is raised. Otherwise Term is ``written'' on Atom
Use Atom as input to read_term/2
using the option
variable_names and return the read term in Term
and the variable bindings in Bindings. Bindings is
a list of
Name = Var couples, thus providing
access to the actual variable names. See also read_term/2.
If Atom has no valid syntax, a
exception is raised.
Atom3 forms the concatenation of Atom1 and Atom2.
At least two of the arguments must be instantiated to atoms, integers or
floating point numbers. For ISO compliance, the instantiation-pattern -,
-, + is allowed too, non-deterministically splitting the 3-th argument
into two parts (as append/3
does for lists). See also
List is a list of atoms, integers or floating point numbers.
Succeeds if Atom can be unified with the concatenated
elements of List. If
List has exactly 2 elements it is equivalent to atom_concat/3,
allowing for variables in the list.
Creates an atom just like concat_atom/2,
but inserts Separator between each pair of atoms. For
?- concat_atom([gnu, gnat], ', ', A).
A = 'gnu, gnat'
Succeeds if Atom is an atom of Length characters
long. This predicate also works for integers and floats, expressing the
number of characters output when given to write/1.
Succeeds if Atom starts with the characters from Prefix.
Its behaviour is equivalent to
?- concat(Prefix, _, Atom),
but avoids the construction of an atom for the `remainder'.
- sub_atom(+Atom, ?Before,
?Len, ?After, ?Sub)
ISO predicate for breaking atoms. It maintains the following relation:
Sub is a sub-atom of Atom that starts at Before,
Len characters and Atom contains After
characters after the match.
?- sub_atom(abc, 1, 1, A, S).
A = 1, S = b
The implementation minimalises non-determinism and creation of atoms.
This is a very flexible predicate that can do search, prefix- and