Hi All, I am very new to Scheme What is wrong with the following code? -------------------------------------------------------------------------------------------------------------------------------- #lang scheme (require rnrs/base-6) (letrec ([my-sum (lambda (l) (if (null? l) 0 (+ (car l) (my-sum (cdr l)))))]) (my-sum '(1 2 3 4))) (define my-sum (lambda (l) (if (null? l) 0 (+ (car l) (my-sum (cdr l)))))) OUTPUT Welcome to DrScheme, version 4.2.1 [3m]. Language: Module; memory limit: 128 megabytes. 10 > (my-sum '(1 2 3)) . . mcar: expects argument of type <mutable-pair>; given (1 2 3) -------------------------------------------------------------------------------------------------------------------------------- If I comment (require rnrs/base-6) or the letrec block the code works as intended -------------------------------------------------------------------------------------------------------------------------------- #lang scheme ;(require rnrs/base-6) (letrec ([my-sum (lambda (l) (if (null? l) 0 (+ (car l) (my-sum (cdr l)))))]) (my-sum '(1 2 3 4))) (define my-sum (lambda (l) (if (null? l) 0 (+ (car l) (my-sum (cdr l)))))) OUTPUT Welcome to DrScheme, version 4.2.1 [3m]. Language: Module; memory limit: 128 megabytes. 10 > (my-sum '(1 2 3)) 6 -------------------------------------------------------------------------------------------------------------------------------- #lang scheme (require rnrs/base-6) #|(letrec ([my-sum (lambda (l) (if (null? l) 0 (+ (car l) (my-sum (cdr l)))))]) (my-sum '(1 2 3 4)))|# (define my-sum (lambda (l) (if (null? l) 0 (+ (car l) (my-sum (cdr l)))))) OUTPUT Welcome to DrScheme, version 4.2.1 [3m]. Language: Module; memory limit: 128 megabytes. > (my-sum '(1 2 3)) 6 -------------------------------------------------------------------------------------------------------------------------------- Am I missing something? Cheers, Ganesh Gunasegaran