# Grammar

The Logtalk grammar is here described using W3C-style Extended Backus-Naur Form syntax. Non-terminal symbols not defined here can be found in the ISO Prolog Core standard. Terminal symbols are represented between double-quotes.

## Entities

    entity ::=
       object
       | category
       | protocol

## Object definition

    object ::=
       begin_object_directive ( object_term )* end_object_directive

    begin_object_directive ::=
       ":- object(" object_identifier ( "," object_relations )? ")."

    end_object_directive ::=
       ":- end_object."

    object_relations ::=
       prototype_relations
       | non_prototype_relations

    prototype_relations ::=
       prototype_relation
       | prototype_relation "," prototype_relations

    prototype_relation ::=
       implements_protocols
       | imports_categories
       | extends_objects

    non_prototype_relations ::=
       non_prototype_relation
       | non_prototype_relation "," non_prototype_relations

    non_prototype_relation ::=
       implements_protocols
       | imports_categories
       | instantiates_classes
       | specializes_classes

## Category definition

    category ::=
       begin_category_directive  ( category_term )* end_category_directive

    begin_category_directive ::=
       ":- category(" category_identifier ( "," category_relations )? ")."

    end_category_directive ::=
       ":- end_category."

    category_relations ::=
       category_relation
       | category_relation "," category_relations

    category_relation ::=
       implements_protocols
       | extends_categories
       | complements_objects

## Protocol definition

    protocol ::=
       begin_protocol_directive  ( protocol_directive )* end_protocol_directive

    begin_protocol_directive ::=
       ":- protocol(" protocol_identifier ( "," extends_protocols)? ")."

    end_protocol_directive ::=
       ":- end_protocol."

## Entity relations

    extends_protocols ::=
       "extends(" extended_protocols ")"

    extends_objects ::=
       "extends(" extended_objects ")"

    extends_categories ::=
       "extends(" extended_categories ")"

    implements_protocols ::=
       "implements(" implemented_protocols ")"

    imports_categories ::=
       "imports(" imported_categories ")"

    instantiates_classes ::=
       "instantiates(" instantiated_objects ")"

    specializes_classes ::=
       "specializes(" specialized_objects ")"

    complements_objects ::=
       "complements(" complemented_objects ")"

### Implemented protocols

    implemented_protocols ::=
       implemented_protocol
       | implemented_protocol_sequence
       | implemented_protocol_list

    implemented_protocol ::=
       protocol_identifier
       | scope "::" protocol_identifier

    implemented_protocol_sequence ::=
       implemented_protocol
       | implemented_protocol "," implemented_protocol_sequence

    implemented_protocol_list ::=
       "[" implemented_protocol_sequence "]"

### Extended protocols

    extended_protocols ::=
       extended_protocol
       | extended_protocol_sequence
       | extended_protocol_list

    extended_protocol ::=
       protocol_identifier
       | scope "::" protocol_identifier

    extended_protocol_sequence ::=
       extended_protocol
       |extended_protocol "," extended_protocol_sequence

    extended_protocol_list ::=
       "[" extended_protocol_sequence "]"

### Imported categories

    imported_categories ::=
       imported_category
       | imported_category_sequence
       | imported_category_list

    imported_category ::=
       category_identifier
       | scope "::" category_identifier

    imported_category_sequence ::=
       imported_category
       | imported_category "," imported_category_sequence

    imported_category_list ::=
       "[" imported_category_sequence "]"

### Extended objects

    extended_objects ::=
       extended_object
       | extended_object_sequence
       | extended_object_list

    extended_object ::=
       object_identifier
       | scope "::" object_identifier

    extended_object_sequence ::=
       extended_object
       | extended_object "," extended_object_sequence

    extended_object_list ::=
       "[" extended_object_sequence "]"

### Extended categories

    extended_categories ::=
       extended_category
       | extended_category_sequence
       | extended_category_list

    extended_category ::=
       category_identifier
       | scope "::" category_identifier

    extended_category_sequence ::=
       extended_category
       | extended_category "," extended_category_sequence

    extended_category_list ::=
       "[" extended_category_sequence "]"

### Instantiated objects

    instantiated_objects ::=
       instantiated_object
       | instantiated_object_sequence
       | instantiated_object_list

    instantiated_object ::=
       object_identifier
       | scope "::" object_identifier

    instantiated_object_sequence ::=
       instantiated_object
       | instantiated_object "," instantiated_object_sequence

    instantiated_object_list ::=
       "[" instantiated_object_sequence "]"

### Specialized objects

    specialized_objects ::=
       specialized_object
       | specialized_object_sequence
       | specialized_object_list

    specialized_object ::=
       object_identifier
       | scope "::" object_identifier

    specialized_object_sequence ::=
       specialized_object
       | specialized_object "," specialized_object_sequence

    specialized_object_list ::=
       "[" specialized_object_sequence "]"

### Complemented objects

    complemented_objects ::=
       object_identifier
       | complemented_object_sequence
       | complemented_object_list

    complemented_object_sequence ::=
       object_identifier
       | object_identifier "," complemented_object_sequence

    complemented_object_list ::=
       "[" complemented_object_sequence "]"

### Entity and predicate scope

    scope ::=
       "public"
       | "protected"
       | "private"

## Entity identifiers

    entity_identifier ::=
       object_identifier
       | protocol_identifier
       | category_identifier

### Object identifiers

    object_identifier ::=
       atom
       | compound

### Category identifiers

    category_identifier ::=
       atom
       | compound

### Protocol identifiers

    protocol_identifier ::=
       atom

### Module identifiers

    module_identifier ::=
       atom

## Source files

    source_file ::=
       ( source_file_content )*

    source_file_content ::=
       source_file_directive
       | clause
       | grammar_rule
       | entity

## Source file names

    source_file_name ::=
       atom
       | library_source_file_name

    library_source_file_name ::=
       library_name "(" atom ")"

    library_name ::=
       atom

## Terms

### Object terms

    object_term ::=
       object_directive
       | clause
       | grammar_rule

### Category terms

    category_term ::=
       category_directive
       | clause
       | grammar_rule

## Directives

### Source file directives

    source_file_directive ::=
       ":- encoding(" atom ")."
       | ":- set_logtalk_flag(" atom "," nonvar ")."
       | ":- include(" source_file_name ")."
       | prolog_directive

### Conditional compilation directives

    conditional_compilation_directive ::=
       ":- if(" callable ")."
       | ":- elif(" callable ")."
       | ":- else."
       | ":- endif."

### Object directives

    object_directive ::=
       ":- initialization(" callable ")."
       | ":- built_in."
       | ":- threaded."
       | ":- dynamic."
       | ":- info(" entity_info_list ")."
       | ":- set_logtalk_flag(" atom "," nonvar ")."
       | ":- include(" source_file_name ")."
       | ":- uses(" object_alias_list ")."
       | ":- use_module(" module_alias_list ")."
       | conditional_compilation_directive
       | predicate_directive

### Category directives

    category_directive ::=
       ":- built_in."
       | ":- dynamic."
       | ":- info(" entity_info_list ")."
       | ":- set_logtalk_flag(" atom "," nonvar ")."
       | ":- include(" source_file_name ")."
       | ":- uses(" object_alias_list ")."
       | ":- use_module(" module_alias_list ")."
       | conditional_compilation_directive
       | predicate_directive

### Protocol directives

    protocol_directive ::=
       ":- built_in."
       | ":- dynamic."
       | ":- info(" entity_info_list ")."
       | ":- set_logtalk_flag(" atom "," nonvar ")."
       | ":- include(" source_file_name ")."
       | conditional_compilation_directive
       | predicate_directive

### Predicate directives

    predicate_directive ::=
       alias_directive
       | synchronized_directive
       | uses_directive
       | use_module_directive
       | scope_directive
       | mode_directive
       | meta_predicate_directive
       | meta_non_terminal_directive
       | info_directive
       | dynamic_directive
       | discontiguous_directive
       | multifile_directive
       | coinductive_directive
       | operator_directive

    alias_directive ::=
       ":- alias(" entity_identifier "," alias_directive_resource_list ")."

    synchronized_directive ::=
       ":- synchronized(" synchronized_directive_resource_term ")."

    uses_directive ::=
       ":- uses(" ( object_identifier | parameter_variable ) "," uses_directive_resource_list ")."

    use_module_directive ::=
       ":- use_module(" ( module_identifier | parameter_variable ) "," use_module_directive_resource_list ")."

    scope_directive ::=
       ":- public(" scope_directive_resource_term ")."
       | ":- protected(" scope_directive_resource_term ")."
       | ":- private(" scope_directive_resource_term ")."

    mode_directive ::=
       ":- mode(" ( predicate_mode_term | non_terminal_mode_term ) "," number_of_proofs ")."

    meta_predicate_directive ::=
       ":- meta_predicate(" meta_predicate_template_term ")."

    meta_non_terminal_directive ::=
       ":- meta_non_terminal(" meta_non_terminal_template_term ")."

    info_directive ::=
       ":- info(" ( predicate_indicator | non_terminal_indicator ) "," predicate_info_list ")."

    dynamic_directive ::=
       ":- dynamic(" qualified_directive_resource_term ")."

    discontiguous_directive ::=
       ":- discontiguous(" qualified_directive_resource_term ")."

    multifile_directive ::=
       ":- multifile(" qualified_directive_resource_term ")."

    coinductive_directive ::=
       ":- coinductive(" ( predicate_indicator_term | coinductive_predicate_template_term ) ")."

    parameter_variable ::=
       _variable_

    scope_directive_resource_term ::=
       scope_directive_resource
       | scope_directive_resource_sequence
       | scope_directive_resource_list

    scope_directive_resource ::=
       predicate_indicator
       | non_terminal_indicator
       | operator

    scope_directive_resource_sequence ::=
       scope_directive_resource
       | scope_directive_resource "," scope_directive_resource_sequence

    scope_directive_resource_list ::=
         "[" scope_directive_resource_sequence "]"

    entity_resources_list ::=
       predicate_indicator_list
       | operator_list

    predicate_indicator_term ::=
       predicate_indicator
       | predicate_indicator_sequence
       | predicate_indicator_list

    predicate_indicator_sequence ::=
       predicate_indicator
       | predicate_indicator "," predicate_indicator_sequence

    predicate_indicator_list ::=
       "[" predicate_indicator_sequence "]"

    alias_directive_resource_list ::=
       "[" alias_directive_resource_sequence "]"

    alias_directive_resource_sequence ::=
       alias_directive_resource
       | alias_directive_resource "," alias_directive_resource_sequence

    alias_directive_resource ::=
       predicate_indicator_alias
       | non_terminal_indicator_alias

    synchronized_directive_resource_term ::=
       synchronized_directive_resource
       | synchronized_directive_resource_sequence
       | synchronized_directive_resource_list

    synchronized_directive_resource ::=
       predicate_indicator
       | non_terminal_indicator

    synchronized_directive_resource_sequence ::=
       synchronized_directive_resource
       | synchronized_directive_resource "," synchronized_directive_resource_sequence

    synchronized_directive_resource_list ::=
       "[" synchronized_directive_resource_sequence "]"

    uses_directive_resource_list ::=
       "[" uses_directive_resource_sequence "]"

    uses_directive_resource_sequence ::=
       uses_directive_resource
       | uses_directive_resource "," uses_directive_resource_sequence

    uses_directive_resource ::=
       predicate_indicator
       | non_terminal_indicator
       | predicate_template_alias
       | operator

    use_module_directive_resource_list ::=
       "[" use_module_directive_resource_sequence "]"

    use_module_directive_resource_sequence ::=
       use_module_directive_resource
       | use_module_directive_resource "," use_module_directive_resource_sequence

    use_module_directive_resource ::=
       predicate_indicator
       | non_terminal_indicator
       | predicate_template_alias
       | operator

    qualified_directive_resource_term ::=
       qualified_directive_resource
       | qualified_directive_resource_sequence
       | qualified_directive_resource_list

    qualified_directive_resource_sequence ::=
       qualified_directive_resource
       | qualified_directive_resource "," qualified_directive_resource_sequence

    qualified_directive_resource_list ::=
       "[" qualified_directive_resource_sequence "]"

    qualified_directive_resource ::=
       predicate_indicator
       | non_terminal_indicator
       | object_identifier "::" ( predicate_indicator | non_terminal_indicator)
       | category_identifier "::" ( predicate_indicator | non_terminal_indicator)
       | module_identifier ":" ( predicate_indicator | non_terminal_indicator)

    predicate_indicator_alias ::=
       predicate_indicator "as" predicate_indicator

    predicate_template_alias ::=
       callable "as" callable

    non_terminal_indicator ::=
       functor "//" arity

    non_terminal_indicator_alias ::=
       non_terminal_indicator "as" non_terminal_indicator

    operator_sequence ::=
       operator specification
       | operator specification "," operator_sequence

    operator_list ::=
       "[" operator_sequence "]"

    coinductive_predicate_template_term ::=
       coinductive_predicate_template
       | coinductive_predicate_template_sequence
       | coinductive_predicate_template_list

    coinductive_predicate_template_sequence ::=
       coinductive_predicate_template
       | coinductive_predicate_template "," coinductive_predicate_template_sequence

    coinductive_predicate_template_list ::=
       "[" coinductive_predicate_template_sequence "]"

    coinductive_predicate_template ::=
       atom "(" coinductive_mode_terms ")"

    coinductive_mode_terms ::=
       coinductive_mode_term
       | coinductive_mode_terms "," coinductive_mode_terms

    coinductive_mode_term ::=
       "+"
       | "-"

    predicate_mode_term ::=
       atom "(" mode_terms ")"

    non_terminal_mode_term ::=
       atom "(" mode_terms ")"

    mode_terms ::=
       mode_term
       |mode_term "," mode_terms

    mode_term ::=
       "@"  type?
       | "+" type?
       | "-" type?
       | "?" type?
       | "++" type?
       | "--" type?

    type ::=
       prolog_type | logtalk_type | user_defined_type

    prolog_type ::=
       "term"
       | "nonvar"
       | "var"
       | "compound"
       | "ground"
       | "callable"
       | "list"
       | "atomic"
       | "atom"
       | "number"
       | "integer"
       | "float"

    logtalk_type ::=
       "object"
       | "category"
       | "protocol"
       | "event"

    user_defined_type ::=
       atom
       | compound

    number_of_proofs ::=
       "zero"
       | "zero_or_one"
       | "zero_or_more"
       | "one"
       | "one_or_more"
       | "zero_or_error"
       | "one_or_error"
       | "zero_or_one_or_error"
       | "zero_or_more_or_error"
       | "one_or_more_or_error"
       | "error"

    meta_predicate_template_term ::=
       meta_predicate_template
       | meta_predicate_template_sequence
       | meta_predicate_template_list

    meta_predicate_template_sequence ::=
       meta_predicate_template
       | meta_predicate_template "," meta_predicate_template_sequence

    meta_predicate_template_list ::=
       "[" meta_predicate_template_sequence "]"

    meta_predicate_template ::=
       object_identifier "::" atom "(" meta_predicate_specifiers ")"
       | category_identifier "::" atom "(" meta_predicate_specifiers ")"
       | module_identifier ":" atom "(" meta_predicate_specifiers ")"
       | atom "(" meta_predicate_specifiers ")"

    meta_predicate_specifiers ::=
       meta_predicate_specifier
       | meta_predicate_specifier "," meta_predicate_specifiers

    meta_predicate_specifier ::=
       non_negative_integer
       | "::"
       | "^"
       | "*"

    meta_non_terminal_template_term ::=
       meta_predicate_template_term

    entity_info_list ::=
       "[" entity_info_sequence? "]"

    entity_info_sequence ::=
       entity_info_item "is" nonvar
       | entity_info_item "is" nonvar "," entity_info_sequence

    entity_info_item ::=
       "comment"
       | "remarks"
       | "author"
       | "version"
       | "date"
       | "copyright"
       | "license"
       | "parameters"
       | "parnames"
       | "see_also"
       | atom

    predicate_info_list ::=
       "[" predicate_info_sequence? "]"

    predicate_info_sequence ::=
       predicate_info_item "is" nonvar
       | predicate_info_item "is" nonvar "," predicate_info_sequence

    predicate_info_item ::=
       "comment"
       | "remarks"
       | "arguments"
       | "argnames"
       | "redefinition"
       | "allocation"
       | "examples"
       | "exceptions"
       | "see_also"
       | atom

    object_alias_list ::=
       "[" object_alias_sequence "]"

    object_alias_sequence ::=
       object_alias
       | object_alias "," object_alias_sequence

    object_alias ::=
       object_identifier "as" object_identifier

    module_alias_list ::=
       "[" module_alias_sequence "]"

    module_alias_sequence ::=
       module_alias
       | module_alias "," module_alias_sequence

    module_alias ::=
       module_identifier "as" module_identifier

## Clauses and goals

    clause ::=
       object_identifier "::" head ":-" body
       | module_identifier ":" head ":-" body
       | head ":-" body
       | object_identifier "::" fact
       | module_identifier ":" fact
       | fact

    goal ::=
       message_sending
       | super_call
       | external_call
       | context_switching_call
       | callable

    message_sending ::=
       message_to_object
       | message_delegation
       | message_to_self

    message_to_object ::=
       receiver "::" messages

    message_delegation ::=
       "[" message_to_object "]"

    message_to_self ::=
       "::" messages

    super_call ::=
       "^^" message

    messages ::=
       message
       | "(" message "," messages ")"
       | "(" message ";" messages ")"
       | "(" message "->" messages ")"

    message ::=
       callable
       | variable

    receiver ::=
       "{" callable "}"
       | object_identifier
       | variable

    external_call ::=
       "{" callable "}"

    context_switching_call ::=
       object_identifier "<<" callable

## Lambda expressions

    lambda_expression ::=
       lambda_free_variables "/" lambda_parameters ">>" callable
       | lambda_free_variables "/" callable
       | lambda_parameters ">>" callable

    lambda_free_variables ::=
       "{" variables? "}"

    lambda_parameters ::=
       "[" terms? "]"

    variables ::=
       variable
       | variable "," variables

    terms ::=
       term
       | term "," terms

## Entity properties

    category_property ::=
       "static"
       | "dynamic"
       | "built_in"
       | "file(" atom ")"
       | "file(" atom "," atom ")"
       | "lines(" integer "," integer ")"
       | "directive(" integer "," integer ")"
       | "events"
       | "source_data"
       | "public(" entity_resources_list ")"
       | "protected(" entity_resources_list ")"
       | "private(" entity_resources_list ")"
       | "declares(" predicate_indicator "," predicate_declaration_property_list ")"
       | "defines(" predicate_indicator "," predicate_definition_property_list ")"
       | "includes(" predicate_indicator "," ( object_identifier | category_identifier ) "," predicate_definition_property_list ")"
       | "provides(" predicate_indicator "," ( object_identifier | category_identifier ) "," predicate_definition_property_list ")"
       | "alias(" ( object_identifier | module_identifier ) "," entity_alias_property_list ")"
       | "alias(" predicate_indicator "," predicate_alias_property_list ")"
       | "calls(" predicate "," predicate_call_update_property_list ")"
       | "updates(" predicate "," predicate_call_update_property_list ")"
       | "number_of_clauses(" integer ")"
       | "number_of_rules(" integer ")"
       | "number_of_user_clauses(" integer ")"
       | "number_of_user_rules(" integer ")"
       | "debugging"

    object_property ::=
       "static"
       | "dynamic"
       | "built_in"
       | "threaded"
       | "file(" atom ")"
       | "file(" atom "," atom ")"
       | "lines(" integer "," integer ")"
       | "directive(" integer "," integer ")"
       | "context_switching_calls"
       | "dynamic_declarations"
       | "events"
       | "source_data"
       | "complements(" ( "allow" | "restrict" ) ")"
       | "complements"
       | "public(" entity_resources_list ")"
       | "protected(" entity_resources_list ")"
       | "private(" entity_resources_list ")"
       | "declares(" predicate_indicator "," predicate_declaration_property_list ")"
       | "defines(" predicate_indicator "," predicate_definition_property_list ")"
       | "includes(" predicate_indicator "," ( object_identifier | category_identifier ) "," predicate_definition_property_list ")"
       | "provides(" predicate_indicator "," ( object_identifier | category_identifier ) "," predicate_definition_property_list ")"
       | "alias(" ( object_identifier | module_identifier ) "," entity_alias_property_list ")"
       | "alias(" predicate_indicator "," predicate_alias_property_list ")"
       | "calls(" predicate "," predicate_call_update_property_list ")"
       | "updates(" predicate "," predicate_call_update_property_list ")"
       | "number_of_clauses(" integer ")"
       | "number_of_rules(" integer ")"
       | "number_of_user_clauses(" integer ")"
       | "number_of_user_rules(" integer ")"
       | "module"
       | "debugging"

    protocol_property ::=
       "static"
       | "dynamic"
       | "built_in"
       | "source_data"
       | "file(" atom ")"
       | "file(" atom "," atom ")"
       | "lines(" integer "," integer ")"
       | "directive(" integer "," integer ")"
       | "public(" entity_resources_list ")"
       | "protected(" entity_resources_list ")"
       | "private(" entity_resources_list ")"
       | "declares(" predicate_indicator "," predicate_declaration_property_list ")"
       | "alias(" predicate_indicator "," predicate_alias_property_list ")"
       | "debugging"

    predicate_declaration_property_list ::=
       "[" predicate_declaration_property_sequence "]"

    predicate_declaration_property_sequence ::=
       predicate_declaration_property
       | predicate_declaration_property "," predicate_declaration_property_sequence

    predicate_declaration_property ::=
       "static"
       | "dynamic"
       | "scope(" scope ")"
       | "private"
       | "protected"
       | "public"
       | "coinductive"
       | "multifile"
       | "synchronized"
       | "meta_predicate(" meta_predicate_template ")"
       | "coinductive(" coinductive_predicate_template ")"
       | "non_terminal(" non_terminal_indicator ")"
       | "include(" atom ")"
       | "lines(" integer  "," integer ")"
       | "line_count(" integer ")"
       | "mode(" ( predicate_mode_term | non_terminal_mode_term ) "," number_of_proofs ")"
       | "info(" list ")"

    predicate_definition_property_list ::=
       "[" predicate_definition_property_sequence "]"

    predicate_definition_property_sequence ::=
       predicate_definition_property
       | predicate_definition_property "," predicate_definition_property_sequence

    predicate_definition_property ::=
       "inline"
       | "auxiliary"
       | "non_terminal(" non_terminal_indicator ")"
       | "include(" atom ")"
       | "lines(" integer  "," integer ")"
       | "line_count(" integer ")"
       | "number_of_clauses(" integer ")"
       | "number_of_rules(" integer ")"

    entity_alias_property_list ::=
       "[" entity_alias_property_sequence "]"

    entity_alias_property_sequence ::=
       entity_alias_property
       | entity_alias_property "," entity_alias_property_sequence

    entity_alias_property ::=
       "object"
       | "module"
       | "for(" ( object_identifier | module_identifier ) ")"
       | "include(" atom ")"
       | "lines(" integer  "," integer ")"
       | "line_count(" integer ")"

    predicate_alias_property_list ::=
       "[" predicate_alias_property_sequence "]"

    predicate_alias_property_sequence ::=
       predicate_alias_property
       | predicate_alias_property "," predicate_alias_property_sequence

    predicate_alias_property ::=
       "predicate"
       | "for(" predicate_indicator ")"
       | "from(" entity_identifier ")"
       | "non_terminal(" non_terminal_indicator ")"
       | "include(" atom ")"
       | "lines(" integer  "," integer ")"
       | "line_count(" integer ")"

    predicate ::=
       predicate_indicator
       | "^^" predicate_indicator
       | "::" predicate_indicator
       | ( variable | object_identifier ) "::" predicate_indicator
       | ( variable | module_identifier ) ":" predicate_indicator

    predicate_call_update_property_list ::=
       "[" predicate_call_update_property_sequence "]"

    predicate_call_update_property_sequence ::=
       predicate_call_update_property
       | predicate_call_update_property "," predicate_call_update_property_sequence

    predicate_call_update_property ::=
       "caller(" predicate_indicator ")"
       | "include(" atom ")"
       | "lines(" integer  "," integer ")"
       | "line_count(" integer ")"
       | "alias(" predicate_indicator ")"
       | "non_terminal(" non_terminal_indicator ")"

## Predicate properties

    predicate_property ::=
       "static"
       | "dynamic"
       | "scope(" scope ")"
       | "private"
       | "protected"
       | "public"
       | "logtalk"
       | "prolog"
       | "foreign"
       | "coinductive(" coinductive_predicate_template ")"
       | "multifile"
       | "synchronized"
       | "built_in"
       | "inline"
       | "recursive"
       | "declared_in(" entity_identifier ")"
       | "defined_in(" ( object_identifier | category_identifier ) ")"
       | "redefined_from(" ( object_identifier | category_identifier ) ")"
       | "meta_predicate(" meta_predicate_template ")"
       | "alias_of(" callable ")"
       | "alias_declared_in(" entity_identifier ")"
       | "non_terminal(" non_terminal_indicator ")"
       | "mode(" ( predicate_mode_term | non_terminal_mode_term ) "," number_of_proofs ")"
       | "info(" list ")"
       | "number_of_clauses(" integer ")"
       | "number_of_rules(" integer ")"
       | "declared_in(" entity_identifier "," line_count ")"
       | "defined_in(" ( object_identifier | category_identifier ) "," line_count ")"
       | "redefined_from(" ( object_identifier | category_identifier ) "," line_count ")"
       | "alias_declared_in(" entity_identifier "," line_count ")"

    line_count ::=
       integer

## Compiler flags

    compiler_flag ::=
       flag "(" flag_value ")"