From-To

Used for primitive types (atoms, numbers, variables).

string_position(From, To)

Used to indicate the position of a string enclosed in double quotes (").

brace_term_position(From, To, Arg)

Term of the form {...}, as used in DCG rules. Arg describes the argument.

list_position(From, To, Elms, Tail)

A list. Elms describes the positions of the elements. If the list specifies the tail as |<TailTerm>, Tail is unified with the term position of the tail, otherwise with the atom none.

term_position(From, To, FFrom, FTo, SubPos)

Used for a compound term not matching one of the above. FFrom and FTo describe the position of the functor. SubPos is a list, each element of which describes the term position of the corresponding subterm.

dict_position(From, To, TagFrom, TagTo, KeyValuePosList)

Used for a dict (see section 5.4). The position of the key-value pairs is described by KeyValuePosList, which is a list of key_value_position/7 terms. The key_value_position/7 terms appear in the order of the input. Because maps do not preserve ordering, the key is provided in the position description.

key_value_position(From, To, SepFrom, SepTo, Key, KeyPos, ValuePos)

Used for key-value pairs in a map (see section 5.4). It is similar to the term_position/5 that would be created, except that the key and value positions do not need an intermediate list and the key is provided in Key to enable synchronisation of the file position data with the data structure.

parentheses_term_position(From, To, ContentPos)

Used for terms between parentheses. This is an extension compared to the original Quintus specification that was considered necessary for secure refactoring of terms.

quasi_quotation_position(From, To, SyntaxTerm, SyntaxPos, ContentPos)

Used for quasi quotations. Given the input {|Syntax||Content|}, SyntaxTerm is the parsed term representation from Syntax, e.g., {|string(X)||Hello {{X}}|} produces Syntax string(X) and SyntaxPos describes the layout of this term. ContentPos is always a term From-To describing the character range of Content.^{114The layout of the term produced by the quasi quotation parser is not available. Future versions may provide an interface that allows contributing a layout term.}

accept

Pass unquoted-atom bytes through verbatim (byte-faithful). This is the default.

nfc

Normalise the text of unquoted atoms (and unquoted functor names) to Unicode NFC before interning, so that two source forms that are canonically equivalent yield the same atom. Requires the kernel normalisation hook; if the hook is not yet registered when this mode is requested (via the option, set_stream/2, the open/4 unicode_atoms option, or the unicode_atoms flag), library(unicode) is loaded automatically. If the library is unavailable the underlying use_module/1 call propagates its existence_error(source_sink, library(unicode)).

error

Raise syntax_error(non_nfc_atom) when an unquoted atom contains text that is not in NFC. Uses the kernel hook for an exact NFC test when library(unicode) is loaded; otherwise falls back to rejecting any code point with wcwidth less than 1 (combining marks, zero-width and non-printable characters), which is conservative but accurate enough for source-code review.

reject

Raise syntax_error(non_ascii_atom) when an unquoted atom contains any non-ASCII code point. Independent of library(unicode).

Quoted atoms and string literals are always byte-faithful, regardless of the mode. This is the canonical description of the four values; the same vocabulary applies to the Prolog flag unicode_atoms, set_stream/2, the unicode_atoms option of open/4, and the unicode_atoms property of stream_property/2.