slightly prettier closure representation.

scm/evalo.scm

        (evalmanyo els env val))]
     [(fresh (x body)
        (== `(lambda (,x) ,body) expr)
        (== `(closure ,x ,body ,env) val))]
        (== `(,expr in ,env) val))]
     [(fresh (e1 e2 x body env^ arg)
        (== `(,e1 ,e2) expr)
        (evalo e1 env `(closure ,x ,body ,env^))
        (evalo e1 env `((lambda (,x) ,body) in ,env^))
        (evalo e2 env arg)
        (evalo body `((,x . ,arg) . ,env^) val))])))