Constant term streams allow the user to consider a constant term (atom, character list or character code list) as a source/sink by associating to them a stream. Reading from a constant term stream will deliver the characters of the constant term as if they had been read from a standard file. Characters written on a constant term stream are stored to form the final constant term when the stream is closed. The built-in predicates described in this section allow the user to open and close a constant term stream for input or output. However, very often, a constant term stream is created to be only read or written once and then closed. To avoid the creation and the destruction of such a stream, GNU Prolog offers several built-in predicates to perform single input/output from/to constant terms (section 7.15).
Templates
Description
open_input_atom_stream(Atom, Stream) unifies Stream with the stream-term which is associated with a new input text-stream whose data are the characters of Atom.
open_input_chars_stream(Chars, Stream) is similar to open_input_atom_stream/2 except that data are the content of the character list Chars.
open_input_codes_stream(Codes, Stream) is similar to open_input_atom_stream/2 except that data are the content of the character code list Codes.
Errors
| Stream is not a variable | type_error(variable, Stream) | |
| Atom is a variable | instantiation_error | |
| Chars is a partial list or a list with an element E which is a variable | instantiation_error | |
| Codes is a partial list or a list with an element E which is a variable | instantiation_error | |
| Atom is neither a variable nor a an atom | type_error(atom, Atom) | |
| Chars is neither a partial list nor a list | type_error(list, Chars) | |
| Codes is neither a partial list nor a list | type_error(list, Codes) | |
| an element E of the Chars list is neither a variable nor a character | type_error(character, E) | |
| an element E of the Codes list is neither a variable nor an integer | type_error(integer, E) | |
| an element E of the Codes list is an integer but not a character code | representation_error(character_code) | |
Portability
GNU Prolog predicates.
Templates
Description
close_input_atom_stream(SorA) closes the constant term stream associated with the stream-term or alias SorA. SorA must a stream open with open_input_atom_stream/2 (section 7.11.1).
close_input_chars_stream(SorA) acts similarly for a character list stream.
close_input_codes_stream(SorA) acts similarly for a character code list stream.
Errors
| SorA is a variable | instantiation_error | |
| SorA is neither a variable nor a stream-term or alias | domain_error(stream_or_alias, SorA) | |
| SorA is not associated with an open stream | existence_error(stream, SorA) | |
| SorA is an output stream | permission_error(close, stream, SorA) | |
| SorA is a stream-term or alias but does not refer to a constant term stream. | domain_error(term_stream_or_alias, SorA) | |
Portability
GNU Prolog predicates.
Templates
Description
open_output_atom_stream(Stream) unifies Stream with the stream-term which is associated with a new output text-stream. All characters written to this stream are collected and will be returned as an atom when the stream is closed by close_ouput_atom_stream/2 (section 7.11.5).
open_output_chars_stream(Stream) is similar to open_output_atom_stream/1 except that the result will be a character list.
open_output_codes_stream(Stream) is similar to open_output_atom_stream/1 except that the result will be a character code list.
Errors
| Stream is not a variable | type_error(variable, Stream) | |
Portability
GNU Prolog predicates.
Templates
Description
close_output_atom_stream(SorA, Atom) closes the constant term stream associated with the stream-term or alias SorA. SorA must be associated with a stream open with open_output_atom_stream/1 (section 7.11.4). Atom is unified with an atom formed with all characters written on the stream.
close_output_chars_stream(SorA, Chars) acts similarly for a character list stream.
close_output_codes_stream(SorA, Codes) acts similarly for a character code list stream.
Errors
| SorA is a variable | instantiation_error | |
| Atom is neither a variable nor an atom | type_error(atom, Atom) | |
| Chars is neither a partial list nor a list | type_error(list, Chars) | |
| Codes is neither a partial list nor a list | type_error(list, Codes) | |
| SorA is neither a variable nor a stream-term or alias | domain_error(stream_or_alias, SorA) | |
| SorA is not associated with an open stream | existence_error(stream, SorA) | |
| SorA is an input stream | permission_error(close, stream, SorA) | |
| SorA is a stream-term or alias but does not refer to a constant term stream | domain_error(term_stream_or_alias, SorA) | |
Portability
GNU Prolog predicates.