Re: [racket-users] Naive question on how to capitalize only the first word of a string

[Glenn Hoetker]

Wow. In addition to getting my question answered, I learned about 6 other 
things.  Thank you so much, everyone!

Glenn

-- 
You received this message because you are subscribed to the Google Groups 
"Racket Users" group.
To unsubscribe from this group and stop receiving emails from it, send an email 
to racket-users+unsubscr...@googlegroups.com.
For more options, visit https://groups.google.com/d/optout.

Re: [racket-users] Naive question on how to capitalize only the first word of a string

[David Storrs]

Here's another:

(define/contract (ucfirst str)
  (-> string? string?)
  (match (regexp-match #px"^([^a-z]*)(.)(.+)" str)
[(list _ prefix first-letter rest-of-string)
 (~a prefix (string-upcase first-letter) rest-of-string)]))

-> (ucfirst "cat dog")
"Cat dog"
-> (ucfirst "  Cat dog")
"  Cat dog"
-> (ucfirst "1  cat dog")
"1  Cat dog"

Modifying the contents of the prefix matcher in the regex will let you
express whatever policy you want.  The one that I've written above is:
'Find the first lower-case Latin character (i.e., a-z) in the string and
change it to uppercase.  Leave the rest of the string otherwise undisturbed'

You could trivially extend the function so that you can change policies on
the fly by passing in the pattern you want:


(define/contract (ucfirst str #:pat [prefix-pat "[^a-z]*"])
  (->* (string?) (#:pat non-empty-string?) string?)
  (define pat (pregexp (~a "^(" prefix-pat ")(.)(.+)")))
  (match (regexp-match pat str)
[(list _ prefix first-letter rest-of-string)
 (~a prefix (string-upcase first-letter) rest-of-string)]
[else str]))

Now this works:

(ucfirst "cat dog")   ; "Cat dog"
(ucfirst "Cat dog")  ; "Cat dog"
(ucfirst "  cat dog"); "  Cat dog"
(ucfirst "cat dog" #:pat "[^aeiou]*") ; "cAt dog"

That last one is a trivial example, but it shows the flexibility you could
easily get.

Now, I wouldn't recommend using the actual code written above.  It's a toy
example intended to demonstrate a technique, not for production.  It's
begging for obtuse errors and/or a string injection attack, since it's
compiling a user-supplied string into a regex and putting metacharacters
around that string.  Still, it shows the flexibility -- ucfirst means
'upcase the first significant character', but the pattern parameter lets
you define what 'significant' means.




On Mon, Jun 19, 2017 at 9:38 PM, Neil Van Dyke  wrote:

> Robby's answer was more idiomatic Racket, and mine was
> idomatic-Scheme-and-also-OK-Racket, by habit. :)
>
> I'd suggest reading both implementations.  As you learn more Racket,
> you'll start to get a feel for your preferred linguistic style(s), and
> you'll notice different people have a lot more stylistic variation than
> just these two.  Also, if you're coming from low-level programming: don't
> worry about micro-optimizing for performance, yet -- performance was one
> head-scratcher that bothered me when I first started learning, but it's
> complicated, and comes later.
>
> Robby also added unit tests, setting a proper example from the start.
>
>
> --
> You received this message because you are subscribed to the Google Groups
> "Racket Users" group.
> To unsubscribe from this group and stop receiving emails from it, send an
> email to racket-users+unsubscr...@googlegroups.com.
> For more options, visit https://groups.google.com/d/optout.
>

-- 
You received this message because you are subscribed to the Google Groups 
"Racket Users" group.
To unsubscribe from this group and stop receiving emails from it, send an email 
to racket-users+unsubscr...@googlegroups.com.
For more options, visit https://groups.google.com/d/optout.

Re: [racket-users] Naive question on how to capitalize only the first word of a string

[Neil Van Dyke]

Robby's answer was more idiomatic Racket, and mine was 
idomatic-Scheme-and-also-OK-Racket, by habit. :)


I'd suggest reading both implementations.  As you learn more Racket, 
you'll start to get a feel for your preferred linguistic style(s), and 
you'll notice different people have a lot more stylistic variation than 
just these two.  Also, if you're coming from low-level programming: 
don't worry about micro-optimizing for performance, yet -- performance 
was one head-scratcher that bothered me when I first started learning, 
but it's complicated, and comes later.


Robby also added unit tests, setting a proper example from the start.

--
You received this message because you are subscribed to the Google Groups "Racket 
Users" group.
To unsubscribe from this group and stop receiving emails from it, send an email 
to racket-users+unsubscr...@googlegroups.com.
For more options, visit https://groups.google.com/d/optout.

Re: [racket-users] Naive question on how to capitalize only the first word of a string

[Jon Zeppieri]

On Mon, Jun 19, 2017 at 8:12 PM, Glenn Hoetker  wrote:
> I'm quite new to Racket/LISP, so I hope this isn't breathtakingly obvious.  
> Can someone please tell me the best way to capitalize just the first word in 
> a multiword string.  So, given the string "it was a dark and stormy night", I 
> would like to get "It was a dark and stormy night". I see functions for 
> turning everything lower case, everything uppercase or capitalizing each 
> word, but nothing in line with what I hope to do.
>
>> (define it "cat dog")
>> (string-titlecase it)
> "Dog Cat"  ; So close, but not quite "Dog cat" as I want.
>
> Many thanks.
>

Yet another option:

#lang racket

(define (cap-first str)
  (match (string->list str)
[(cons x xs)
 (list->string
  (cons (char-upcase x) xs))]
[_
 str]))

-- 
You received this message because you are subscribed to the Google Groups 
"Racket Users" group.
To unsubscribe from this group and stop receiving emails from it, send an email 
to racket-users+unsubscr...@googlegroups.com.
For more options, visit https://groups.google.com/d/optout.

Re: [racket-users] Naive question on how to capitalize only the first word of a string

[Robby Findler]

Here's another way to implement it. Fun. :)

#lang racket

(provide
 (contract-out
  [cap-first (-> string? string?)]))

(define (cap-first s)
  (apply
   string
   (for/list ([c (in-string s)]
  [i (in-naturals)])
 (if (= i 0)
 (char-upcase c)
 c

(module+ test
  (require rackunit)
  (check-equal? (cap-first "") "")
  (check-equal? (cap-first "Cat dog") "Cat dog")
  (check-equal? (cap-first "cat dog") "Cat dog"))


Robby

On Mon, Jun 19, 2017 at 7:40 PM, Neil Van Dyke  wrote:
> Welcome to Racket!
>
> One intro-to-Racket-compared-to-some-other-languages thing I'll just say
> upfront is that you don't want to modify the string itself, not that you
> asked to.  (Not all Racket strings are mutable.  Plus, mutating introduces a
> bunch more possibilities for bugs, and for string operations, we usually are
> in the "pure functional" school of thought.  There are rare situations in
> which you'll want to mutate strings, but that's an advanced topic, after
> comfortable with idiomatic Racket.)
>
> I'm not aware of this particular procedure in base Racket, so here's one
> implementation.  Someone new to Racket might like to read through this
> procedure and try to figure out the thinking of how the language and
> standard library was used.
>
> (define (string-capitalize str)
>   (or (string? str)
>   (raise-argument-error 'capitalize
> "string?"
> str))
>   (if (equal? "" str)
>   str
>   (let ((first-char (string-ref str 0)))
> (if (char-lower-case? first-char)
> (string-append (string (char-upcase first-char))
>(substring str 1))
> str
>
> Note that this assumes that the first character of the string is also the
> first character of any first word.  If there might be whitespace or other
> non-alphabetic characters before a lowercase alphabetic character, and your
> policy would be to find the start of the word, then you'd probably want to
> document the exact policy, and then code a loop to check successive
> characters (until a determining character or the end of string is found).
>
>
> --
> You received this message because you are subscribed to the Google Groups
> "Racket Users" group.
> To unsubscribe from this group and stop receiving emails from it, send an
> email to racket-users+unsubscr...@googlegroups.com.
> For more options, visit https://groups.google.com/d/optout.

-- 
You received this message because you are subscribed to the Google Groups 
"Racket Users" group.
To unsubscribe from this group and stop receiving emails from it, send an email 
to racket-users+unsubscr...@googlegroups.com.
For more options, visit https://groups.google.com/d/optout.

Re: [racket-users] Naive question on how to capitalize only the first word of a string

[Neil Van Dyke]

Welcome to Racket!

One intro-to-Racket-compared-to-some-other-languages thing I'll just say 
upfront is that you don't want to modify the string itself, not that you 
asked to.  (Not all Racket strings are mutable.  Plus, mutating 
introduces a bunch more possibilities for bugs, and for string 
operations, we usually are in the "pure functional" school of thought.  
There are rare situations in which you'll want to mutate strings, but 
that's an advanced topic, after comfortable with idiomatic Racket.)


I'm not aware of this particular procedure in base Racket, so here's one 
implementation.  Someone new to Racket might like to read through this 
procedure and try to figure out the thinking of how the language and 
standard library was used.


(define (string-capitalize str)
  (or (string? str)
  (raise-argument-error 'capitalize
"string?"
str))
  (if (equal? "" str)
  str
  (let ((first-char (string-ref str 0)))
(if (char-lower-case? first-char)
(string-append (string (char-upcase first-char))
   (substring str 1))
str

Note that this assumes that the first character of the string is also 
the first character of any first word.  If there might be whitespace or 
other non-alphabetic characters before a lowercase alphabetic character, 
and your policy would be to find the start of the word, then you'd 
probably want to document the exact policy, and then code a loop to 
check successive characters (until a determining character or the end of 
string is found).


--
You received this message because you are subscribed to the Google Groups "Racket 
Users" group.
To unsubscribe from this group and stop receiving emails from it, send an email 
to racket-users+unsubscr...@googlegroups.com.
For more options, visit https://groups.google.com/d/optout.

Re: [racket-users] Naive question on how to capitalize only the first word of a string

[Philip McGrath]

I don't think there's a library function that does what you want, so you'd
need to define your own. Here's one way to do it:

(define (capitalize-first-letter str)
  (cond
[(non-empty-string? str)
 (define first-letter-str
   (substring str 0 1))
 (define rest-str
   (substring str 1 (string-length str)))
 (string-append (string-upcase first-letter-str)
rest-str)]
[else
 ""]))

-Philip

On Mon, Jun 19, 2017 at 5:12 PM, Glenn Hoetker  wrote:

> I'm quite new to Racket/LISP, so I hope this isn't breathtakingly
> obvious.  Can someone please tell me the best way to capitalize just the
> first word in a multiword string.  So, given the string "it was a dark and
> stormy night", I would like to get "It was a dark and stormy night". I see
> functions for turning everything lower case, everything uppercase or
> capitalizing each word, but nothing in line with what I hope to do.
>
> > (define it "cat dog")
> > (string-titlecase it)
> "Dog Cat"  ; So close, but not quite "Dog cat" as I want.
>
> Many thanks.
>
>
> --
> You received this message because you are subscribed to the Google Groups
> "Racket Users" group.
> To unsubscribe from this group and stop receiving emails from it, send an
> email to racket-users+unsubscr...@googlegroups.com.
> For more options, visit https://groups.google.com/d/optout.
>

-- 
You received this message because you are subscribed to the Google Groups 
"Racket Users" group.
To unsubscribe from this group and stop receiving emails from it, send an email 
to racket-users+unsubscr...@googlegroups.com.
For more options, visit https://groups.google.com/d/optout.

[racket-users] Naive question on how to capitalize only the first word of a string

[Glenn Hoetker]

I'm quite new to Racket/LISP, so I hope this isn't breathtakingly obvious.  Can 
someone please tell me the best way to capitalize just the first word in a 
multiword string.  So, given the string "it was a dark and stormy night", I 
would like to get "It was a dark and stormy night". I see functions for turning 
everything lower case, everything uppercase or capitalizing each word, but 
nothing in line with what I hope to do.

> (define it "cat dog")
> (string-titlecase it)
"Dog Cat"  ; So close, but not quite "Dog cat" as I want.

Many thanks.


-- 
You received this message because you are subscribed to the Google Groups 
"Racket Users" group.
To unsubscribe from this group and stop receiving emails from it, send an email 
to racket-users+unsubscr...@googlegroups.com.
For more options, visit https://groups.google.com/d/optout.