/* Part of SWI-Prolog Author: Jan Wielemaker E-mail: J.Wielemaker@vu.nl WWW: http://www.swi-prolog.org Copyright (C): 2013, VU University Amsterdam This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this library; if not, write to the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA As a special exception, if you link this library with other files, compiled with a Free Software compiler, to produce an executable, this library does not by itself cause the resulting executable to be covered by the GNU General Public License. This exception does not however invalidate any other reasons why the executable file might be covered by the GNU General Public License. */ :- module(quasi_quotations, [ with_quasi_quotation_input/3, % +Content, -Stream, :Goal phrase_from_quasi_quotation/2, % :Grammar, +Content quasi_quotation_syntax_error/1, % +Error quasi_quotation_syntax/1 % :Syntax ]). :- use_module(library(error)). :- use_module(library(pure_input)). :- use_module( library(lists) ). /** Define Quasi Quotation syntax @ingroup swi Inspired by [Haskell](http://www.haskell.org/haskellwiki/Quasiquotation), SWI-Prolog support _quasi quotation_. Quasi quotation allows for embedding (long) strings using the syntax of an external language (e.g., HTML, SQL) in Prolog text and syntax-aware embedding of Prolog variables in this syntax. At the same time, quasi quotation provides an alternative to represent long strings and atoms in Prolog. The basic form of a quasi quotation is defined below. Here, `Syntax` is an arbitrary Prolog term that must parse into a _callable_ (atom or compound) term and Quotation is an arbitrary sequence of characters, not including the sequence =||}|=. If this sequence needs to be embedded, it must be escaped according to the rules of the target language or the `quoter' must provide an escaping mechanism. == {|Syntax||Quotation|} == While reading a Prolog term, and if the Prolog flag =quasi_quotes= is set to =true= (which is the case if this library is loaded), the parser collects quasi quotations. After reading the final full stop, the parser makes the call below. Here, `SyntaxName` is the functor name of `Syntax` above and `SyntaxArgs` is a list holding the arguments, i.e., `Syntax =.. [SyntaxName|SyntaxArgs]`. Splitting the syntax into its name and arguments is done to make the quasi quotation parser a predicate with a consistent arity 4, regardless of the number of additional arguments. == call(+SyntaxName, +Content, +SyntaxArgs, +VariableNames, -Result) == The arguments are defined as - `SyntaxName` is the principal functor of the quasi quotation syntax. This must be declared using quasi_quotation_syntax/1 and there must be a predicate SyntaxName/4. - `Content` is an opaque term that carries the content of the quasi quoted material and position information about the source code. It is passed to with_quasi_quote_input/3. - `SyntaxArgs` carries the additional arguments of the `Syntax`. These are commonly used to make the parameter passing between the clause and the quasi quotation explicit. For example: == ..., {|html(Name, Address)|| NameAddress |} == - `VariableNames` is the complete variable dictionary of the clause as it is made available throug read_term/3 with the option =variable_names=. It is a list of terms `Name = Var`. - `Result` is a variable that must be unified to resulting term. Typically, this term is structured Prolog tree that carries a (partial) representation of the abstract syntax tree with embedded variables that pass the Prolog parameters. This term is normally either passed to a predicate that serializes the abstract syntax tree, or a predicate that processes the result in Prolog. For example, HTML is commonly embedded for writing HTML documents (see library(http/html_write)). Examples of languages that may be embedded for processing in Prolog are SPARQL, RuleML or regular expressions. The file library(http/http_quasiquotations) provides the, suprisingly simple, quasi quotation parser for HTML. @author Jan Wielemaker. Introduction of Quasi Quotation was suggested by Michael Hendricks. @see [Why it's nice to be quoted: quasiquoting for haskell](http://www.eecs.harvard.edu/~mainland/ghc-quasiquoting/mainland07quasiquoting.pdf) */ :- meta_predicate with_quasi_quotation_input(+, -, 0), quasi_quotation_syntax(4), phrase_from_quasi_quotation(//, +). :- set_prolog_flag(quasi_quotations, true). %% with_quasi_quotation_input(+Content, -Stream, :Goal) is det. % % Process the quasi-quoted Content using Stream parsed by Goal. % Stream is a temporary stream with the following properties: % % - Its initial _position_ represents the position of the % start of the quoted material. % - It is a text stream, using =utf8= _encoding_. % - It allows for repositioning % - It will be closed after Goal completes. % % @arg Goal is executed as once(Goal). Goal must succeed. % Failure or exceptions from Goal are interpreted as % syntax errors. % @see phrase_from_quasi_quotation/2 can be used to process a % quatation using a grammar. with_quasi_quotation_input(Content, Stream, Goal) :- functor(Content, '$quasi_quotation', 3), !, setup_call_cleanup( '$qq_open'(Content, Stream), ( call(Goal) -> true ; quasi_quotation_syntax_error( quasi_quotation_parser_failed, Stream) ), close(Stream)). %% phrase_from_quasi_quotation(:Grammar, +Content) is det. % % Process the quasi quotation using the DCG Grammar. Failure of % the grammer is interpreted as a syntax error. % % @see with_quasi_quotation_input/3 for processing quotations from % stream. phrase_from_quasi_quotation(Grammar, Content) :- functor(Content, '$quasi_quotation', 3), !, setup_call_cleanup( '$qq_open'(Content, Stream), phrase_quasi_quotation(Grammar, Stream), close(Stream)). phrase_quasi_quotation(Grammar, Stream) :- set_stream(Stream, buffer_size(512)), stream_to_lazy_list(Stream, List), phrase(Grammar, List), !. phrase_quasi_quotation(_, Stream) :- quasi_quotation_syntax_error( quasi_quotation_parser_failed, Stream). %% quasi_quotation_syntax(:SyntaxName) is det. % % Declare the predicate SyntaxName/4 to implement the the quasi % quote syntax SyntaxName. Normally used as a directive. quasi_quotation_syntax(M:Syntax) :- must_be(atom, Syntax), '$set_predicate_attribute'(M:Syntax/4, quasi_quotation_syntax, 1). %% quasi_quotation_syntax_error(+Error) % % Report syntax_error(Error) using the current location in the % quasi quoted input parser. % % @throws error(syntax_error(Error), Position) quasi_quotation_syntax_error(Error) :- quasi_quotation_input(Stream), quasi_quotation_syntax_error(Error, Stream). quasi_quotation_syntax_error(Error, Stream) :- stream_syntax_error_context(Stream, Context), throw(error(syntax_error(Error), Context)). quasi_quotation_input(Stream) :- '$input_context'(Stack), memberchk(input(quasi_quoted, _File, _Line, StreamVar), Stack), Stream = StreamVar. %% stream_syntax_error_context(+Stream, -Position) is det. % % Provide syntax error location for the current position of % Stream. stream_syntax_error_context(Stream, file(File, LineNo, LinePos, CharNo)) :- stream_property(Stream, file_name(File)), position_context(Stream, LineNo, LinePos, CharNo), !. stream_syntax_error_context(Stream, stream(Stream, LineNo, LinePos, CharNo)) :- position_context(Stream, LineNo, LinePos, CharNo), !. stream_syntax_error_context(_, _). position_context(Stream, LineNo, LinePos, CharNo) :- stream_property(Stream, position(Pos)), !, stream_position_data(line_count, Pos, LineNo), stream_position_data(line_position, Pos, LinePos), stream_position_data(char_count, Pos, CharNo). /******************************* * SYSTEM HOOK * *******************************/ % system:'$parse_quasi_quotations'(+Quotations:list, +Module) is % det. % % @arg Quotations is a list of terms % % quasi_quotation(Syntax, Quotation, VarNames, Result) :- public system:'$parse_quasi_quotes'/2. system:'$parse_quasi_quotations'([], _). system:'$parse_quasi_quotations'([H|T], M) :- qq_call(H, M), system:'$parse_quasi_quotations'(T, M). qq_call(quasi_quotation(Syntax, Content, VariableNames, Result), M) :- current_prolog_flag(sandboxed_load, false), Syntax =.. [SyntaxName|SyntaxArgs], setup_call_cleanup( '$push_input_context'(quasi_quoted), call(M:SyntaxName, Content, SyntaxArgs, VariableNames, Result), '$pop_input_context'), !. qq_call(quasi_quotation(Syntax, Content, VariableNames, Result), M) :- current_prolog_flag(sandboxed_load, true), Syntax =.. [SyntaxName|SyntaxArgs], Expand =.. [SyntaxName, Content, SyntaxArgs, VariableNames, Result], QExpand = M:Expand, '$expand':allowed_expansion(QExpand), setup_call_cleanup( '$push_input_context'(quasi_quoted), call(QExpand), '$pop_input_context'), !. qq_call(quasi_quotation(_Syntax, Content, _VariableNames, _Result), _M) :- setup_call_cleanup( '$push_input_context'(quasi_quoted), with_quasi_quotation_input( Content, Stream, quasi_quotation_syntax_error(quasi_quote_parser_failed, Stream)), '$pop_input_context'), !. /******************************* * MESSAGES * *******************************/ :- multifile prolog:error_message//1. prolog:error_message(syntax_error(unknown_quasi_quotation_syntax(Syntax, M))) --> { functor(Syntax, Name, _) }, [ 'Quasi quotation syntax ~q:~q is not defined'-[M, Name] ]. prolog:error_message(syntax_error(invalid_quasi_quotation_syntax(Syntax))) --> [ 'Quasi quotation syntax must be a callable term. Found ~q'-[Syntax] ].