Douglas Burke > Inline-SLang > Inline::SLang

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NAME ^

Inline::SLang - Write Perl subroutines in S-Lang.

SYNOPSIS ^

  use Inline SLang;

  print "9 + 16 = ", add(9,16), "\n";
  print "9 - 16 = ", subtract(9,16), "\n";
  print JAxH('Inline'), "\n";

  __END__
  __SLang__

  define add      (a,b) { return a + b; }
  define subtract (a,b) { return a - b; }
  define JAxH () {
    variable type = ();
    return sprintf( "Just Another %S Hacker!", type );
  }

DESCRIPTION ^

The Inline::SLang module lets you write Perl subroutines in S-Lang. It dynamically translates the parameters and return values into native data types for both languages (or into Perl classes that are used to represent S-Lang types with no direct translation to Perl). This allows you to write a Perl script and take advantage of S-Lang whenever you wish: perhaps there is a S-Lang module that you wish to use, or you want to take advantage of a S-Lang function that you have written.

The module sets up an in-process S-Lang interpreter, runs your code, and then examines the interpreter's symbol table, looking for things to bind to Perl. The process of interrogating the S-Lang interpreter only occurs the first time you run your S-Lang code. The namespaces are cached, and subsequent calls use the cached version (which is hidden in the _Inline directory; see the Inline documentation for details of how the code is cached). Of course, your S-Lang code must still be run every time your run the Perl script -- but Inline::S-Lang already knows the results of running it.

What is S-Lang? ^

From the S-Lang library home page at http://www.s-lang.org/

S-Lang is a multi-platform programmer's library designed to allow a developer to create robust multi-platform software. It provides facilities required by interactive applications such as display/screen management, keyboard input, keymaps, and so on. The most exciting feature of the library is the slang interpreter that may be easily embedded into a program to make it extensible.

For our purposes it is the S-Lang interpreter that we are interested in. See the Term::Slang module (on CPAN) if you want an interface to the terminal library provided by S-Lang.

Using the Inline::SLang Module ^

Using Inline::SLang will seem very similar to using any other Inline language, thanks to Inline's consistent look and feel.

This section will explain the different ways to use Inline::SLang. Further details on configuring the behaviour of Inline::SLang can be found in Inline::SLang::Config. For more details on Inline, see Inline or perldoc Inline.

S-Lang Functions

Using functions defined in S-Lang is just like using Perl subroutines. You just supply the source code to Inline::SLang - see the Inline manual for the various ways of doing this - and then use them in your Perl code. For example:

   # set up a S-Lang function
   use Inline SLang => <<'END';
   define doit() { vmessage("Printing from S-Lang"); }
   END

   # now call the S-Lang function from Perl
   doit;

By default all S-Lang functions - other than S-Lang intrinsic functions (the functions defined by the S-Lang interpreter, such as array_map() and assoc_get_keys()) - in the default namespace ("Global") are bound to Perl. The Perl functions are available in the main package.

The BIND_NS configuration option can be used to change the list of S-Lang namespaces bound to Perl. If you have need of an intrinsic S-Lang function then you can either write a wrapper routine or use the BIND_SLFUNCS option. See Inline::SLang::Config for more details.

Note that there are no checks that a S-Lang symbol, when mapped to Perl, does not clobber an existing value (or is a Perl built-in function so can not be over-ridden). So beware when you define a S-Lang function called open()!

But all I want to do is use a S-Lang module?

If you have a S-Lang module that you want to use directly from Perl, it's as easy as the following (assuming the module is importable and called funkymodule):

  use Inline 'SLang' => 'import("funkymodule");';

and then you can start using the functions defined by the module. You use a similar technique if you have a file containing S-Lang code that can be loaded using require or evalfile: e.g.

  use Inline 'SLang' => 'require("funkypackage");';

The use of the require() function is only possible if your S-Lang installation includes the slsh interpreter and ancillary files (which is true if you use CIAO 3.2).

S-Lang Variables

We do not bind any S-Lang variables to Perl. To access variables you have to write S-Lang routines that read/write the variable, as shown by the get_foobar() and set_foobar() routines below:

  variable foobar = "a string";
  define get_foobar()  { return foobar; }
  define set_foobar(x) { foobar = x; }

Supported Data Types

Inline::S-Lang attempts to seamlessly convert between Perl and S-Lang data types. For "simple" types - for example strings - where there is a direct match between S-Lang and Perl, the conversion is not noticeable. For more complicated types - such as complex numbers - S-Lang variables are converted to Perl objects. Where possible a perl-like interface is retained. See Inline::SLang::Types for more information on how the various data types are supported.

The module currently requires that yor S-Lang library has been compiled with support for both floating-point and complex numbers.

Perl routines

The module provides several utility functions which are discussed below. By default they are only available using fully-qualified names - e.g. Inline::SLang::sl_eval() - although the EXPORT configuration option can be used to change this.

Inline::SLang::sl_array

Usage:

  $sl = Inline::SLang::sl_array( $aref );
  $sl = Inline::SLang::sl_array( $aref, $adims );
  $sl = Inline::SLang::sl_array( $aref, $atype );
  $sl = Inline::SLang::sl_array( $aref, $adims, $atype );

This is a wrapper around the Array_Type constructor and is intended to make it easy to ensure that a Perl array reference is converted into a S-Lang array of the correct type, dimensionality, and size.

The data is stored in $aref, a Perl array reference. If no other parameters are supplied then the array dimensions, size, and type are guessed from $aref. Since Perl has such a flexible type system the routine can sometimes make a surprising choice for the data type of the array, so it may well be worth supplying the array type as $atype - which can be either a string containing the name of the S-Lang datatype, such as "Int_Type", or a DataType_Type object.

If you know the array dimensions then it's probably faster to supply them as the $adims argument, which should be an array reference.

Note that there is limited error checking in this routine: if $aref is a 2x3 array but you send in $adims as [3,2] - or [24] say - then expect weird behaviour (at the very least).

Example:

  use Inline 'SLang' => Config => EXPORT => [ "sl_array" ];
  use Inline 'SLang';
  ...
  some_slang_func( sl_array([[1.0,0.0],[0.0,1.0]],"Double_Type") );

For numeric types I expect most people to use piddles. This routine is more useful for arrays of non-numeric data types.

Inline::SLang::sl_array2perl

Usage:

  $val = Inline::SLang::sl_array2perl();
  $val = Inline::SLang::sl_array2perl( $newval );

Sets/Gets the current status of the "how do we convert a S-Lang array into Perl" flag. Returns the status.

We list the possible values of the flag below. For further details on array support in Inline::SLang see Inline::SLang::Array.

With no PDL support

If PDL support was not compiled in to the module then the flag can either be 0 or 1, where

Value = 0

All arrays are converted to a Perl array reference.

Value = 1

All arrays are converted to a Perl Array_Type object

With PDL support

If PDL support is available then there are four options:

Value = 0

All arrays are converted to a Perl array reference.

Value = 1

All arrays are converted to a Perl Array_Type object

Value = 2

Numeric arrays are converted to piddles and non-numeric arrays are converted to a Perl array reference.

Value = 3

Numeric arrays are converted to piddles and non-numeric arrays are converted to a Perl Array_Type object.

Inline::SLang::sl_eval

Usage

  [ retval(s) = ] Inline::SLang::sl_eval( $str );

This function evaluates the supplied S-Lang code (in $str) and converts any return values to Perl. In general this will not be needed, since you can always call S-Lang's eval() function via a wrapper function (or by binding it to a different function name in Perl). One approach is shown in the last example below.

One time it can come in useful is to access a S-Lang variable (either to set its value or store its value in a Perl variable).

If $str does not end with a ";" then one will be added before the code is evaluated by S-Lang.

Examples:

  # get the version of the S-Lang library
  my $sl_ver = Inline::SLang::sl_eval( "_slang_version" );

  # set a variable in S-Lang scope (assuming this_var exists in
  # S-Lang scope)
  Inline::SLang::sl_eval( "this_var = 23.5" );

  # evaluate arbitrary S-Lang code
  my $foo = Inline::SLang::sl_eval("23+4");
  print "S-Lang thinks 23+4 is $foo\n";

A more flexible solution is to write a S-lang wrapper around the S-Lang eval() function (perhaps this functionality should be moved into sl_eval?):

  % Call as myeval( "slang code" [, var1, var2, ... ] );
  % where varX are variables that placed onto the S-Lang
  % stack before calling the S-Lang code
  define myeval() {
    % pop off the slang code from the stack, leave the rest there
    variable slcode;
    if ( _NARGS > 1 ) {
      _stk_reverse(_NARGS);
      slcode = ();
      _stk_reverse(_NARGS-1);
    }
    else
      slcode = ();
    eval( slcode );
  }

Inline::SLang::sl_have_pdl

Usage:

  $flag = Inline::SLang::sl_have_pdl();

Returns 1 if the module was compiled with support for PDL, and 0 otherwise.

Inline::SLang::sl_setup_as_slsh()

Usage:

  Inline::SLang::sl_setup_as_slsh();

This routine sets up the S-Lang interpreter to use the same paths as the slsh interpreter from the S-Lang distribution. It is called by the module when the SETUP configuration option is set to slsh, which is the default value. It is very unlikely that a user will have a need to call this routine directly.

Inline::SLang::sl_setup_called()

Usage:

  $counter = Inline::SLang::sl_setup_called();

Returns the number of times the sl_setup_slsh() function has been called. In most cases this will return 1 if the SETUP configuration option was set to slsh - the default value - and 0 otherwise.

Inline::SLang::sl_typeof

Usage:

  $type = Inline::SLang::sl_typeof( $var );

Returns the S-Lang type of the data stored in the Perl variable $var. This should be more efficient than using S-Lang's typeof() command since it does not require the conversion of the whole variable to S-Lang (normally not a big issue but it can be if $var contains a large array or a complicated structure).

The return value is an object of the DataType_Type class; see PDL::Types for more information on how S-Lang variables are represented in Perl.

Example:

  my $foo = some_slang_function();
  my $type = Inline::SLang::sl_typeof($foo);
  print "The function returned a $type variable\n";

Note that all objects used to represent S-Lang data types - other than Math::Complex objects - have a typeof() method which can be used to find the type of the object.

Inline::SLang::sl_version

Usage:

  $ver = Inline::SLang::sl_version();

Returns, as a string, the version of S-Lang against which the module was compiled, with a format of "a.b.c". You can use sl_eval("_slang_version_string") to find out what version of the library you are using.

What happens when there is a S-Lang error?

The module will refuse to build if there is an error in the S-Lang code compiled when your program is first run. If an error occurs in the S-Lang interpreter - such as calling a function that expects an argument with none - then the S-Lang error is transformed into a Perl error (as a call to croak) and the S-Lang interpreter is restarted. This means that these errors can be handled by using Perl's eval statement. For example, the code

  use strict;
  use Inline 'SLang';

  # Call the S-Lang function
  #
  my $ans;
  eval { $ans = mydiv (0.0); };
  print "The S-Lang error was:\n$@\n";

  # Evaluate S-Lang code directly
  #
  eval { Inline::SLang::sl_eval( "10.0/0.0;" ); };
  print "The S-Lang error was:\n$@\n";

  __END__
  __SLang__

  define mydiv(y) { return 10.0 / y; }

(which can be found in the distribution as examples/trap_errors.pl) produces the following output:

  The S-Lang error was:
  S-Lang Error: Divide by zero: Error while executing mydiv

  The S-Lang error was:
  S-Lang Error: Divide by zero: called from line 1, file: ***string***

CHANGES ^

v1.00 Tue Jan 4 12:02:37 EST 2005

The S-Lang interpreter can now be initialised in a similar manner to that used in the slsh interpreter from the S-Lang distribution. This was primarily added to support the changes made to the S-Lang support in CIAO 3.2 - e.g. the use of require() to load modules - but may be useful elsewhere. This does not add the functions and variables added by slsh, e.g.: __argc, __argv, exit(), atexit(), and stat_mode_to_string().

This support is on by default but can be turned off by adding

  use Inline SLang => CONFIG => 'none';

to your script.

General documentation clean up (mainly minor changes). Added examples/trap_errors.pl to the distribution.

The list of changes to previous versions has been moved to Inline::SLang::Changes.

SUPPORTED PLATFORMS ^

BUGS AND DEFICIENCIES ^

Please use the CPAN Resource Tracker at http://rt.cpan.org/NoAuth/Bugs.html?Dist=Inline-SLang to check for bugs, report new ones, and request new features.

SEE ALSO ^

Inline::SLang::Config, Inline::SLang::Changes, Inline::SLang::Types, Inline::SLang::Array, Inline::SLang::Assoc, Inline::SLang::Struct, Inline::SLang::Details, Term::Slang

For information about using Inline, see Inline.

For information about other Inline languages, see Inline-Support.

For information about S-Lang see http://www.s-lang.org/.

ACKNOWLEDGEMENTS ^

John Davis (for S-Lang), Brian Ingerson (for the Inline framework), and Neil Watkiss since I based much of this module on his Inline::Python and Inline::Ruby modules.

However, please do not assume that any errors in this module are in any way related to the above people.

AUTHOR ^

Doug Burke <djburke@cpan.org>

COPYRIGHT ^

This software is Copyright (C) 2003, 2004, 2005 Smithsonian Astrophysical Observatory. All rights are reserved.

It is released under the GNU General Public License. You may find a copy of this licence in the file LICENSE within the source distribution or at http://www.fsf.org/copyleft/gpl.html

Prior to version 0.04 the module was distributed under the same terms as Perl.

WARRANTY ^

There is no warranty. Please see the GNU General Public License for more details.

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