Re: [racket-users] Replacing multiple characters in a string?

[William G Hatch]

Or, arguably, not Rackety enough, until it's possible to embed one #lang within 
another (submodules at least, but hey why not lambdas?)


I've been exploring this more and more.  It is related to my shell
project (rash, which does allow embedding at the expression level), and
I've been thinking about it a lot in relation to other things I want to
do or have otherwise been considering.  Some time soon I'll have to
write up my thoughts on the subject.

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Re: [racket-users] Replacing multiple characters in a string?

[Robby Findler]

Keep reading?

#lang lindenmayer racket

## axiom ##
ABCABC

## rules ##
A -> AC
B -> BA
C -> CCA

## variables ##
n=1


(provide A B C start finish)
(define (finish l vars) (writeln l))
(define (A s vars) (cons 'A s))
(define (B s vars) (cons 'B s))
(define (C s vars) (cons 'C s))
(define (start var) '())




On Sat, Jul 8, 2017 at 2:38 PM, Matthew Butterick  wrote:
>
>
>> On Jul 8, 2017, at 7:15 AM, Robby Findler  
>> wrote:
>>
>> Below is another approach that may be too much Rackety for your taste:  :)
>>
>> http://docs.racket-lang.org/lindenmayer/
>
> Or, arguably, not Rackety enough, until it's possible to embed one #lang 
> within another (submodules at least, but hey why not lambdas?)
>
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Re: [racket-users] Replacing multiple characters in a string?

[Matthew Butterick]

> On Jul 8, 2017, at 7:15 AM, Robby Findler  wrote:
> 
> Below is another approach that may be too much Rackety for your taste:  :)
> 
> http://docs.racket-lang.org/lindenmayer/
 
Or, arguably, not Rackety enough, until it's possible to embed one #lang within 
another (submodules at least, but hey why not lambdas?)

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Re: [racket-users] Replacing multiple characters in a string?

[David Storrs]

I'd probably do this:

(apply string-append
  (for/list ((letter (string->list str)))
 (cond [(equal? letter #\A) "AC"]
   [(equal? letter #\B) "BA"]
   [(equal? letter #\C) "CCA"])))

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Re: [racket-users] Replacing multiple characters in a string?

[Robby Findler]

Below is another approach that may be too much Rackety for your taste:  :)

http://docs.racket-lang.org/lindenmayer/

Robby


#lang lindenmayer

## axiom ##
ABCABC

## rules ##
A -> AC
B -> BA
C -> CCA

## variables ##
n=1

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Re: [racket-users] Replacing multiple characters in a string?

[Philip McGrath]

This works, for instance (and I would much prefer case to hash-ref):

#lang typed/racket

(regexp-replace* #rx"[ABC]"
 "ABCABC"
 (λ ([c : String] . _)
   (case c
 [("A") "AC"]
 [("B") "BA"]
 [("C") "CCA"]
 [else (error 'bad-match c)])))

-Philip

On Sat, Jul 8, 2017 at 8:14 AM, Alasdair McAndrew  wrote:

> Many thanks - that works fine!  And it makes sense, to use regexp-replace*
> with a hash table.  (All these things I'm still finding out...)  Is it
> possible to do this - or something similar - in Typed Racket?
>
> On Saturday, 8 July 2017 22:45:04 UTC+10, Neil Van Dyke  wrote:
> > This is one OK way that people are likely to do:
> >
> >
> > #lang racket/base
> >
> > (define (foo str)
> >(regexp-replace* #rx"[ABC]"
> > str
> >(lambda (s)
> >  (hash-ref #hash(("A" . "AC")
> >  ("B" . "BA")
> >  ("C" . "CCA"))
> >s
> >
> > (module+ test
> >(require rackunit)
> >(check-equal? (foo "") "")
> >(check-equal? (foo "ABCABC")   "ACBACCAACBACCA")
> >(check-equal? (foo "ABCDABCD") "ACBACCADACBACCAD"))
> >
> >
> > It's not necessarily the most maintainable (note the duplicated info
> > between the regexp and the map) nor most efficient, but it's OK, IMHO.
>
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Re: [racket-users] Replacing multiple characters in a string?

[Alasdair McAndrew]

Many thanks - that works fine!  And it makes sense, to use regexp-replace* with 
a hash table.  (All these things I'm still finding out...)  Is it possible to 
do this - or something similar - in Typed Racket?

On Saturday, 8 July 2017 22:45:04 UTC+10, Neil Van Dyke  wrote:
> This is one OK way that people are likely to do:
> 
> 
> #lang racket/base
> 
> (define (foo str)
>(regexp-replace* #rx"[ABC]"
> str
>(lambda (s)
>  (hash-ref #hash(("A" . "AC")
>  ("B" . "BA")
>  ("C" . "CCA"))
>s
> 
> (module+ test
>(require rackunit)
>(check-equal? (foo "") "")
>(check-equal? (foo "ABCABC")   "ACBACCAACBACCA")
>(check-equal? (foo "ABCDABCD") "ACBACCADACBACCAD"))
> 
> 
> It's not necessarily the most maintainable (note the duplicated info 
> between the regexp and the map) nor most efficient, but it's OK, IMHO.

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Re: [racket-users] Replacing multiple characters in a string?

[Neil Van Dyke]

This is one OK way that people are likely to do:


#lang racket/base

(define (foo str)
  (regexp-replace* #rx"[ABC]"
   str
  (lambda (s)
(hash-ref #hash(("A" . "AC")
("B" . "BA")
("C" . "CCA"))
  s

(module+ test
  (require rackunit)
  (check-equal? (foo "") "")
  (check-equal? (foo "ABCABC")   "ACBACCAACBACCA")
  (check-equal? (foo "ABCDABCD") "ACBACCADACBACCAD"))


It's not necessarily the most maintainable (note the duplicated info 
between the regexp and the map) nor most efficient, but it's OK, IMHO.


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[racket-users] Replacing multiple characters in a string?

[Alasdair McAndrew]

Suppose I have a string "ABCABC" and I want to replace all A's with "AC", all 
B's with "BA" and all C's with "CCA", so that the result is

ACBACCAACBACCA

What is the canonical way of doing this in Racket?  

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