[Mulgara-dev] in clauses in trans/walk constraints

[Life is hard, and then you die]

We just noticed that while the sablecc grammar allows an 'in' clause
in trans/walk constraints, as in

    walk(<a:1> <b:1> $o in <m:1> and $s <b:1> $o in <m:1>)

the ConstraintExpressionBuilder, line 786, throws an exception if
there's an 'in' clause. Looking at the code it isn't clear to me why
this is being prohibited. Any clues? Or can the check be removed?


  Cheers,

  Ronald