r_call.pl -- R plugin for SWISH

This module make R available to SWISH using the Rserve R package. The module r_serve.pl implements a SWI-Prolog wrapper around the Rserve C++ client to realise the communication with the R server.

The Prolog view at R is inspired by real from Nicos Angelopoulos.

It consists of the following two predicates:

• Var <- Expression Assign the result of evaluating the given R Expression to Var. Var can be a Prolog variable or an R expression.
• <- Expression Evaluate expression, discarding the result. Possible console output is captured.

In addition, the quasi quotation r is defined. The quasi quotation takes Prolog variables as arguments and an R expression as content. Arguments (Prolog variable names) that match R identifiers cause the temporary of an R variable with that name bound to the translated Prolog value. R quasi quotations can be used as isolated goals, as well as as right-hand arguments to <-/2 and <-/1. The example below calls the R plot() function on the given Prolog list.

?- numlist(1,10,Data),
   {|r(Data)||plot(Data)|}.

Images created by the R session are transferred as SVG and sent to the SWISH console using pengine_output/1.

 <-(Var, Expression) is det

Assign the result of evaluating the given R Expression to Var. Var can be a Prolog variable or an R expression.

 <-(Expression) is det

Evaluate Expression, discarding the result. Possible console output is captured using the R function capture.output.

 r_call(+Fun, +Options)

Construct and possibly call an R function. Fun can be an atom or a compound, eg plot, or plot(width=3). The predicate also supports multiple output destinations. Options processed:

call(Bool)

If false (default true), do not call the result.

fcall(-Term)

Term is unified with the constructed call

rvar(Var)

Variable for the output

Compatibility

- This is a partial implementation of the corresponding real predicate.

 r_console(+Stream, ?Term)[multifile]

Hook console interaction. Currently only used for <-/1 to emit the captured output. In this cases, Stream is stdout and Term is a list of strings, each representing a line of output. The list can be empty. If the hook fails, maplist(writeln, Term) is called to write the output to current_output.

 r_execute(+Assignments, +Command, -Result) is det

Execute the R command Command after binding the variables in Assignments and unify the result with Result.

Arguments:

Assignments	- is a list of Name=Value, where Name must be a valid R indentifier.
Command	- is a string holding the R command to execute

 r(+Content, +Vars, +VarDict, -Goal) is det

Parse {|r(Arg,...||R-code|} into a the expression below. This expression may be passed to <-/2 and <-/1 as well as used directly as a goal, calling r_execute/3.

r_execute(Assignments, Command, Result)

See also

- https://cran.r-project.org/doc/manuals/r-release/R-lang.html#Parser

To be done

- Verify more of the R syntax.

 rserve:r_open_hook(+Name, -R)[multifile]

Called for lazy creation to the Rserve server. Connections are per-thread. The destination depends on settings:

Unix domain socket

If rserve:socket is defined and not empty, it is taken as the path to a Unix domain socket to connect to.

TCP/IP socket

Else, if rserve:port and rserve:host is defined, we connect to the indicated host and port.

After the connection is established, the session can be configured using the hook r_init_session/1. The default calls r_setup_graphics/2 to setup graphics output to send SVG files.

 r_init_session(+RConn) is semidet[multifile]

Multifile hook that is called after the Rserve server has handed us a new connection. If this hook fails, r_setup_graphics/2 is called to setup capturing graphics as SVG files.

 r_setup_graphics(+Rconn, +Format) is det

Setup graphics output using files. Currently only supports Format = svg.

 r_display_images(+Images:list)[multifile]

Hook to display images.

Arguments:

Images

- is a list of images. Each image is of the form Format(String), where Format is the file extension. Currently only uses svg. If not defined, print_message/2 is called with the term r_images(Images).