
source_read(+SourcePos, -NextPos, -Kind, -SourceTerm)

   Read the next term from an open ECLiPSe source file

Arguments
   SourcePos           Source position handle
   NextPos             Source position handle
   Kind                kind of source term (atom)
   SourceTerm          a source_term structure

Type
   library(source_processor)

Description
This reads the next source term from a source file previously
    opened with source_open/3. The term at the current source position
    SourcePos is read, and the next source position is returned for use
    in subsequent source_read/4 invocations (it is not possible to read
    twice from the same source position!).
    
    The term that has been read is classified into one of the following
    categories (Kind):
    
    handled_directive
    	A directive (a term with functor :-/1) which has already
	been handled (interpreted by source_read/4). Such directives are:
	module/1,3, local/1, export/1, reexport/1, use_module/1, lib/1,
	pragma/1, include/1, ./2, op/3, meta_attribute/2 and
	comment(include,...)
    directive
    	A directive (a term with functor :-/1) which has not
	been handled (ignored by source_read/4)
    query
    	A query (a term with functor ?-/1)
    clause
    	Any other structure, list or atom (usually a clause)
    var
    	A term consisting of only a variable (very likely an error)
    other
    	A number, string, etc (very likely an error)
    comment
    	Spacing, layout and comments between source terms
    	(only when keep_comments option is in effect)
    end_include
    	The end of an included source file
    end
    	The end of the (top-level) source file
    
    The information about the source term itself is returned as a structure
    
    :- export struct(source_term(
	term,		% the read term itself
	vars,		% list of [VarName|Var] pairs (as in readvar/3)
	annotated       % the read term with type and source annotations 
	...
    )).
    
    For category 'comment', the term is a string containing the comment.
    For category 'end' and 'end_include', the term is the atom end_of_file.
    In all these cases, vars is the empty list, and annotated is
    uninstantiated.
    
    Note that either the vars-field or the annotated field is valid,
    depending on the setting of the with_annotations-option.  If the option
    is set, the vars field contains an empty list, and the annotated term
    is in the same format as that returned by read_annotated/2, i.e. a
    recursive wrapper structure around the read term of the following format:

    :- export struct(annotated_term(
        term,                   % var, atomic or compound
                                % args of compound terms are annotated
        type,                   % term type (see below)
        file,                   % file name (atom)
        line,                   % line number (integer >= 1)
        from, to                % source position (integers >= 0)
        ...
    )).

    If the with_annotations-option is not set, the annotated-field remains
    uninstantiated, and the vars-field is a list as detailed in readvar/3.
    
    Notes on module handling:  When source_read/4 encounters a
    module-directive (which is a handled_directive), the corresponding
    module is implicitly created (unless it exists already, in which
    case it is either reused or erased and re-created, depending on
    the setting of the recreate_modules option), and that
    module becomes the context module for any subsequently read
    clauses or directives.  By default, source_close/2 removes these
    modules again in order to restore the original state.
    

See Also
   source_open / 3, source_close / 2, readvar / 3, read_annotated / 2
