The soft stack version of the interpreter reports counts of 5 different sorts of subexpression evaluation and also how much storage was used, and how much is available on the free list. The sorts are
report labelsort of expression
var<ident>
invoke prim funf in (fa) where f is primordial
invoke lam funf in (fa) where f is a value produced by evaluation a λ-expression
lambda(λxb)
numeral42