sicp-exs/sicp-ex-1.30.rkt

#! /usr/bin/racket
#lang racket/base

(define (sum term a next b)
  (define (iter a result)
    (if (> a b)
      result
      (iter (next a) (+ (term a) result))))
  (iter a 0))

(sum (lambda (x) x) 0 (lambda (x) (+ x 1)) 3)