Extending the &OpenMath; package
Exploring the range of supported symbols
OMsymRecord

The &OpenMath; package supports such basic &OpenMath; objects as integers ( <OMI> ), character strings ( <OMSTR> ) and variables ( <OMVAR> ). Besides that, it supports a number of &OpenMath; content dictionaries (some of them only partially, dependently on their relevance to &GAP;).

To see which symbols from which content dictionaries are supported for the conversion from &OpenMath; to &GAP;, explore the global record OMsymRecord. Its components have names of appropriate CDs, and subcomponents of each component have names of symbols from the corresponding CD. If the value of the component is not equal to fail, then it contains the function or the object which is used for conversion. The following example of the entry for the nums1 CD demonstrates a combination of all possible cases:

gap> Print(OMsymRecord.nums1,"\n"); rec( e := fail, i := E(4), pi := fail, based_integer := fail, gamma := fail, infinity := infinity, NaN := fail, rational := function ( x ) return OMgapId( [ OMgap2ARGS( x ), x[1] / x[2] ] )[2]; end )
OMsymRecord
contains all symbols for which conversion from &OpenMath; to &GAP; is supported except some special symbols related with errors and special procedures from the &SCSCP; package which are treated separately.

To check quickly if &GAP; can parse a given &OpenMath; object, copy the &OpenMath; code and paste it directly into standard input after the following commands:

gap> stream := InputTextUser();; gap> g := OMGetObject(stream);CloseStream(stream);

The main tool for the conversion from &GAP; to &OpenMath; is OMPut( <stream>, <object> ). A number of methods for OMPut are installed in the file openmath/gap/omput.gi.

To check quickly whether the object may be converted to &OpenMath;, call OMprint for that object, for example:

gap> OMPrint( [ [1..10], ZmodnZObj(2,6), (1,2) ] ); <OMOBJ> <OMA> <OMS cd="list1" name="list"/> <OMA> <OMS cd="interval1" name="integer_interval"/> <OMI> 1</OMI> <OMI> 10</OMI> </OMA> <OMA> <OMS cd="integer2" name="class"/> <OMI> 2</OMI> <OMI> 6</OMI> </OMA> <OMA> <OMS cd="permut1" name="permutation"/> <OMI> 2</OMI> <OMI> 1</OMI> </OMA> </OMA> </OMOBJ>

The package is in the continuous development and will support even more symbols in the future. In the meantime, if you will have any requests for the support for particular symbols, please write to Alexander Konovalov who currently develops and maintains the package.

Adding support for private content dictionaries and symbols

There is also a way for the user to extend the package adding support for private and experimental CDs or separate symbols. We allocated the directory openmath/private for this purposes, and currently it contain the file private.g for conversions from &OpenMath; to &GAP; and the file private.gi for conversions from &GAP; to &OpenMath; for some symbols from private CDs contained in the openmath/cds directory.

In particular, we extended the package with the following private &OpenMath; symbols: group1.group_by_generators which allows us to input and output groups given by their generators as this is a natural way to create groups in &GAP;; semigroup1.semigroup_by_generators and monoid1.monoid_by_generators following the same considerations for semigroups and monoids; pcgroup1.pcgroup_by_pcgscode for PcGroups given by their pcgs code and order; record1.record for records as they are important data structures which we want to pass in a straightforward manner between different &GAP; instances; transform1.transformation to support transformations, transformation semigroups and their automorphism groups.

The file private.g is loaded from openmath/gap/new.g, and the private.gi is loaded from openmath/gap/read.g. If the user would like to add own code, this may be done either by adding it to these files or by placing additional files in openmath/private directory and load them similarly to private.g and private.gi.

We will welcome user's contributions in the form of the code to support existing content dictionaries from the &OpenMath; web site or private content dictionaries, if they may be interesting for a wider community.