Whee. partcl now passes along unknown commands to the shell as its big brother does:
$ make tclsh
% echo "whee"
This done as I've committed a per6 grammar for [expr], which when run through the demo for PGE seems to work just fine: problem is being able to get at this data programmatically afterward. it's a bit convoluted, hopefully I can build on what autrijus has done in PGE.hs