How to format output using racket

Question

How do I format output using racket? I want to output a fixed-width number and fill it with 0 if the width is too small? How can I do it? I have searched the racket documentation but I can only find fprintf, which seems to be unable to do it.

Answer 1

You can use functions from the racket/format module. For example ~a:

#lang racket
(require racket/format)
(~a 42 
    #:align 'right
    #:width 4
    #:pad-string "0")

returns

"0042"

Answer 2

format in #!racket isn't as rich as sprintf in C languages. A workaroundwould eb to do it yourself:

(require srfi/13)
(string-pad (number->string 23) 4 #\0) ; ==> "0023"