read/[1,2]

Module: sio

read/1 — read a term from the current input stream
read/2 — read a term from specified stream
read_term/2 — read term from current input with options
read_term/3 — read term from specified stream with options

ISO Standard Predicate

FORMS

read(Term)

read(Stream_or_Alias, Term)


read_term(Term, Options)

read_term(Stream_or_Alias, Term, Options)

DESCRIPTION

These predicates are used to read a term from a stream using the operator declarations in effect at the time of the read. The end of the term read from the stream is indicated by a fullstop token appearing in the stream. The fullstop token is a period(‘ . ‘) followed by a newline, white space character, or line comment character. If the stream is positioned so that there are no more terms to be read and the stream has the property eof_action(eof_code), then Term will be unified with the atom end_of_file.

read/1 reads a term from the current input stream and unifies it with Term.

read/2 reads a term from the input stream specified by Stream_or_Alias and unifies it with Term.

read_term/2 reads a term from the current input stream with options Options (see below) and unifies the term read with Term.

read_term/3 reads a term from the input stream specified by Stream_or_Alias and unifies it with Term. The options specified by Options are used in the process of reading the term.

read_term/2 and read_term/3 take the parameter Options which is a list of options to read_term. These options either affect the behavior of read_term or are used to retrieve additional information about the term which was read.

The following options supported by ALS Prolog are options specified by the March’93 ISO Prolog Standard:

The following additional options are supported by ALS Prolog:

EXAMPLES

?- read(Term).
[+(3,4),9+8]. << Typed on console (current input)

Term=[3+4,9+8]

yes.

?- read_term(Term,[variables(V),variable_names(VN),singletons(SVN)]).
f(X,[Y,Z,W],g(X,Z),[_,U1,_,U2]). << Typed on console (current input)

Term=f(_A,[_B,_C,_D],g(_A,_C),[_E,_F,_G,_H]) 
V=[_A,_B,_C,_D,_E,_F,_G,_H] 
VN=[_A = 'X',_B = 'Y',_C = 'Z',_D = 'W',_F = 'U1',_H = 'U2'] 
SVN=[_B = 'Y',_D = 'W',_F = 'U1',_H = 'U2'] 

yes.
?- open(atom('[X,2,3]'),read,S),
?_ read_term(S,Term,[attach_fullstop(true)]), close(S).

S=stream_descriptor('\002',closed,atom,atom('[X,2,3]'),[input|nooutput],
    false,42,'[X,2,3]',7,7,0,true,0,wt_opts(78,400,flat),[],wait,text,
    eof_code,true,0) 
Term=[_A,2,3] 

yes.
?- read_term(user_input,Term,not_an_option_list). 
Error: Argument of type list expected instead of not_an_option_list.
- Goal:          sio:read_term(user_input,_A,not_an_option_list)
- Throw pattern: error(type_error(list,not_an_option_list),
                     [sio:read_term(user_input,_A,not_an_option_list)])

?- read(X).
foobar << Typed on console (current input)
zipper. << Typed on console (current input)

zipper.
^Syntax error 
	'standard input', line 9: Fullstop (period) expected

ERRORS

Stream_or_Alias is a variable

– – – – > instantiation_error.

Stream_or_Alias is neither a variable nor a stream descriptor nor an alias

– – – – > domain_error(stream_or_Alias, Stream_or_Alias) .

Stream_or_Alias is not associated with an open stream

– – – – > existence_error(stream, Stream_or_Alias) .

Stream_or_Alias is not an input stream

– – – – > permission_error(input, stream, Stream_or_Alias) .

Options is a variable

– – – – > instantiation_error.

Options is neither a variable nor a list

– – – – > type_error(list, Option) .

Options is a list an element of which is a variable

– – – – > instantiation_error.

Options is a list containing an element E which is neithera variable nor a valid read option

– – – – > domain_error(read_option, E)

The stream associated with Stream_or_Alias is at the end of the stream and the stream has the property eof_action(error)

– – – – > existence_error(past_end_of_stream, Stream_or_Alias) .

The stream associated with Stream_or_Alias has no input ready to be read and the stream has the property snr_action(error)

– – – – > existence_error(stream_not_ready, Stream_or_Alias) .

SEE ALSO