I've mistyped. In fact things are even worse.
#lang racket
(define-syntax U
(syntax-rules ()
[(_ f) (f f)]))
(define-syntax define/comb
(syntax-rules ()
[(_ comb name (arg . args) f)
(define name
(comb (λ (name) (λ (arg . args) f))))]))
(define (Z f)
(U (λ (g) (λ x
(apply (f (U g)) x)))))
(define/comb Z comb-sum (l t)
(if (empty? l) t (comb-sum (rest l) (+ t (first l)))))
(define (sum l t)
(if (empty? l) t (sum (rest l) (+ t (first l)))))
(time (comb-sum (make-list 10000000 1) 0))
(time (sum (make-list 10000000 1) 0))
Result:
cpu time: 9922 real time: 10007 gc time: 3323
10000000
cpu time: 2762 real time: 2783 gc time: 469
10000000
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