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 label	sort of expression
var	<ident>
invoke prim fun	f in (fa) where f is primordial
invoke lam fun	f in (fa) where f is a value produced by evaluation a λ-expression
lambda	(λxb)
numeral	42