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read_term(+Stream, -Term, ++Options)

Read a whole term in ECLiPSe syntax from the input stream Stream, according to Options

Stream: Stream handle or alias (atom)
Term: An term, usually a variable
Options: List of option terms

Description

This is a generalisation of the read/2 predicate (and deprecated predicates read_annotated/2,3, readvar/3). It reads one term in ECLiPSe syntax from the input stream Stream, and returns it as Term. Options is a (possibly empty) list of the following options:

annotated(-AnnTerm): returns AnnTerm, which is a compound annotated_term{} that is structurally similar to Term and contains all information about Term, plus additional type information, variable names, and source position annotations for all subterms. For details see read_annotated/3.
line(-Line): returns the Stream line number where Term starts.
variables(-Vars): returns a duplicate-free list of all the variables in Term (including anonymous variables).
variable_names(-VarsNames): returns a duplicate-free list of structures of the form Name=Var, where Var is a named (non-anonymous) variable which occurs in Term, and Name is an atom, representing the source name.
singletons(-VarsNames): returns a list of structures of the form Name=Var, where Var is a named (non-anonymous) variable which occurs only once in Term, and Name is an atom, representing the source name.
syntax_errors(+Atom): modifies the treatment of syntax errors: if 'quiet', the predicate fails quietly; if 'fail', an error message is printed and then the predicate fails; if 'error', a term of the form error(syntax_error(MessageString),context(...)) is thrown. The default is 'fail' if the per-module syntax_option 'syntax_errors_fail' is set, otherwise 'error'.

Modes and Determinism

read_term(+, -, ++) is semidet

Modules

This predicate is sensitive to its module context (tool predicate, see @/2).

Fail Conditions

Fails if a syntax error was detected and no term could be read

Exceptions

(4) instantiation fault: Stream is not instantiated.
(5) type error: Stream is not an atom or a stream handle.
(5) type error: Options is not a list of compound terms.
(6) out of range: Options list contains a unrecognised option.
(192) illegal stream mode: Stream is not an input stream.
(193) illegal stream specification: Stream is an illegal stream specification.

Examples

        ?- read_term(T, []).
         foo(X,_,bar(X,Y,_Z)).

        T = foo(X, _255, bar(X, Y, _Z))


        ?- read_term(T, [variable_names(VN)]).
         foo(X,_,bar(X,Y,_Z)).

        T = foo(X, _260, bar(X, Y, _Z))
        VN = ['X' = X, 'Y' = Y, '_Z' = _Z]


        ?- read_term(T, [variables(V),variable_names(VN),singletons(S)]).
         foo(X,_,bar(X,Y,_Z)).

         T = foo(X, _278, bar(X, Y, _Z))
         V = [X, _278, Y, _Z]
         VN = ['X' = X, 'Y' = Y, '_Z' = _Z]
         S = ['_Z' = _Z, 'Y' = Y]

        ?- read_term(T, [syntax_errors(quiet)]).
	a b.
	No (0.00s cpu)

        ?- read_term(T, [annotated(AT)]).
        foo(3,X).

        T = foo(3, X)
        AT = annotated_term(foo(
                     annotated_term(3, integer, user, 1, 4, 5),
                     annotated_term(X, var('X'), user, 1, 6, 7)),
                 compound, user, 1, 0, 4)