Section "atom"

We make the content of a host language string, which is also our datatype of a Prolog atom visible as a list of Unicode points. The string encoding of the host language is made transpar-ent. The built-ins do not expose the string encoding. This translates also to the Prolog characters codes and atoms used by streams in the next section.

There can be nevertheless differences among host languages. For example we find differences in term_hash/2 for supplementary code points that require surrogate pairs in UTF-16 encoding, whereas in an UTF-32 encoding they only occupy one element. Further lexical compare might give different results for private use area.

The following atom built-ins are provided:

atom_codes(A, L): [ISO 8.16.5]

If A is a variable, the built-in succeeds in A with the for the Prolog list L. Otherwise the built-in succeeds in L with the Prolog list from the atom A.

char_code(C, N): [ISO 8.16.6]

If C is a variable, the built-in succeeds in C with the character for the code N. Otherwise the built-in succeeds in N with the code from character C.

atom_number(A, N):

If A is a variable, then the built-in succeeds in A with the atom for the Prolog number N. Otherwise the built-in succeeds in N with the Prolog number from the atom A.

atom_integer(A, R, N):

If A is a variable, then the built-in succeeds in A with the atom for the Prolog integer N in radix R. Otherwise the built-in succeeds in N with the Prolog number from the atom A in radix R.

atom_length(X, Y): [ISO 8.16.1]

The predicate succeeds in Y with the length of the atom X.atom_concat(X, Y, Z): [ISO 8.16.2]
The built-in succeeds when Z is the concatenation of X and Y.

sub_atom(X, Y, Z, T, U): [ISO 8.16.3]

The predicate succeeds whenever the atom U is the sub atom of the atom X starting at position Y with length Z and ending T characters before.

last_sub_atom(X, Y, Z, T, U):

The predicate succeeds whenever the atom U is the sub atom of the atom X starting at position Y with length Z and ending T characters before.

atom_join(L, A):

The built-in succeeds in A with the join of the atoms L.

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