J. Ian Johnson wrote at 09/01/2011 09:43 AM:
I have a list of symbols '(a b c) that I want to be printed "a b c" as part of
string I'm formatting.
If you don't mind parentheses, you can do: (format "~s" syms)
I think that "format" has conspicuously avoided getting like C "printf"
or the super-scary CL function. It's convenient for what it is, and is
not intended to be anything more than what it is.
I think there are some formatting libraries in PLaneT.
One thing to keep in mind as you're formatting things: if you want to do
be formatting huge outputs, you'll want to be writing incrementally to a
port, not making a massive string. Below is a little code I just banged
out to illustrate writing formatting code that scales. It's not
intended to be a gee-whiz demo. ("You have to write all that code just
to put spaces in a list?!")
#lang racket
;; Sometimes it's preferable to write formatting procedures that first
;; write to ports rather than generate strings...
(define (display-list-items/separator lst
separator
(out (current-output-port)))
(or (null? lst)
(let loop ((item (car lst))
(lst (cdr lst)))
(write item out)
(if (null? lst)
(void)
(begin (display separator out)
(loop (car lst) (cdr lst)))))))
;; Then you can combine it with other output procedures, and it scales
;; to arbitrary size of output...
(define (write-report lst out)
;; TODO: Write a gigabyte of earlier report text here.
(display "This is my list: {" out)
(display-list-items/separator lst ", " out)
(display "}\n" out)
;; TODO: Write some more report text here.
)
;; For dealing with small outputs, you can make a wrapper for the
;; writing procedure that returns a string...
(define (list-items->string/separator lst separator)
(call-with-output-string
(lambda (out)
(display-list-items/separator lst separator out))))
;; Obligatory tests...
(require (planet neil/overeasy:1:0))
(test (format "~a" (string-join (map symbol->string '(a b c)) " "))
"a b c")
(test (list-items->string/separator '(a b c) " ")
"a b c")
(test (list-items->string/separator '(a b c) ", ")
"a, b, c")
(test (list-items->string/separator '() " ")
"")
--
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