Hi,
I recently started using Racket and i couldn't find a good alternative to C's
scanf/printf in the racket standard library. When doing programming challenges,
you often need to comply to a specific input/ouput thus having something like
scanf for string to values and printf for values to string is comfy.
For example, let's say a challenge where you simply have to output the input
but you need to translate the strings input into values and then those values
back to strings.
The given input(and excepted ouput) is
3
[04, foo, 03.5]
[05, bar, 04.6]
[06, fun, 05.7]
In C, you would simply do
#include <stdio.h>
int main(void)
{
int n;
// Read number of rows
scanf("%d\n", &n);
// Output number of rows
printf("%d\n", n);
// Process rows
for (unsigned int i; i < n; ++i)
{
int a;
char b[20];
float c;
// Read row
scanf("[%d, %[^,], %f]\n", &a, b, &c);
// Output row
printf("[%02d, %s, %04.1f]\n", a, b, c);
}
}
Now, for a solution in Racket, You first have to read the first line and
convert it into a number.
(define rows (string->number (read-line)))
Then, for all rows, read and split the string. The best that i have found to do
that is using regular expressions.
(define split-row (regexp-match #rx"\\[(.+), (.+), (.+)\\]" (read-line)))
Then you have to manually convert the substrings into values
(define a (string->number (second split-row)))
(define b (third split-row))
(define c (string->number (fourth split-row)))
Then you have to manually convert the values back into strings
(printf "[~a, ~a, ~a]\n"
(~a a #:width 2 #:align 'right #:pad-string "0")
b
(~r c #:min-width 4 #:precision 1 #:pad-string "0")))
This is way more tedious than with the classical input/output format,
especially when you are doing coding challenges.
Final Racket solution:
#lang racket
(define rows (string->number (read-line)))
(for ([in-range rows])
(define split-row (regexp-match #rx"\\[(.+), (.+), (.+)\\]" (read-line)))
(define a (string->number (second split-row)))
(define b (third split-row))
(define c (string->number (fourth split-row)))
(printf "[~a, ~a, ~a]\n"
(~a a #:width 2 #:align 'right #:pad-string "0")
b
(~r c #:min-width 4 #:precision 1 #:pad-string "0")))
Having something like (not necessary the same specifiers as with printf)
(string-scan "[%d, %s, %f]" "[45, foo, 10.9]") -> '(45 "foo" 10.9)
and a proper output formatter would be comfy.
Are racket devs against such a thing in the standard library ?
How you guys are actually doing IO in racket ?
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