Ah OK, I understand that additional newline. Since the code matching the
regex is run before that newline gets in, the newline will be on the
input port.
In DrRacket I observe the following:
(I remembered that there are negative numbers :D and my regex got a bit
more complicated.)
~~~
(regexp-try-match #rx"\\s*^(-?[1-9]+[0-9]*)$|\\s*^0$" (current-input-port))
~~~
When I run it the first time, I get the "input box" where I can click
the "EOF" button on the right and the regex seems to work. When I try
again immediately after, the first time, there is still an #<eof> on the
port, which apparently was not consumed, so it will immediately return
#f. I can get rid of that #<eof> by running (read-line) once. On REPL
line I would have a newline and in DrRacket I have an #<eof>.
On REPL it does not stop expecting input, because it never receives an
#<eof>. I read somewhere on Stackoverflow that I input #<eof> by
pressing Ctrl+d and that may be true, but it does not work in REPL,
because that shuts down the REPL. So basically it seems impossible to
test such regular expressions on REPL.
I think I will instead use:
~~~
(let ([something (read-line (current-input-port) 'any)])
(... do regex things on finished string here ...))
~~~
to work around this problem in the future. This will actually finish the
line at any marker of a new line and then let me work with the regex
more comfortably. Also instead of running it in the REPL, I will
probably run a small program instead with racket <racket file>.
Thanks for clearing up my confusion!
I tried to write this in Typed Racket and the following is what I got.
This works:
~~~
(: get-input-number (-> Integer))
(define (get-input-number)
(let loop : Integer ()
(let ([something (read-line (current-input-port) 'any)])
(cond [(string? something)
(let ([number-representation (string->number something)])
(cond [(exact-integer? number-representation)
number-representation]
[else (printf "nope~n")
(loop)]))]
[else (printf "nope~n")
(loop)]))))
(get-input-number)
~~~
While the following does not work:
~~~
(define (get-input-number-2)
(let loop : Integer ()
(let* ([something (read-line (current-input-port) 'any)]
[match-res (regexp-match #rx"(^-?[1-9]+[0-9]*$)|(^0$)" something)])
(cond [(string? something)
(let ([number-representation (string->number something)])
(cond [(exact-integer? number-representation)
number-representation]
[else (printf "nope~n")
(loop)]))]
[else (printf "nope~n")
(loop)]))))
(get-input-number-2)
~~~
The opening paren of regexp-match is underlined and when I run this code
I get the lengthy error message:
~~~
main.rkt:34:22: Type Checker: No function domains matched in function
application:
Domains: (U Byte-Regexp Bytes Regexp String) (U Bytes Input-Port)
Integer (U False Integer) (U False Output-Port) Bytes #f *
(U Byte-Regexp Bytes Regexp String) (U Bytes Input-Port)
Integer (U False Integer) (U False Output-Port) #f *
(U Byte-Regexp Bytes Regexp String) (U Bytes Input-Port)
Integer (U False Integer) #f *
(U Byte-Regexp Bytes Regexp String) (U Bytes Input-Port)
Integer #f *
(U Byte-Regexp Bytes Regexp String) (U Bytes Input-Port) #f *
(U Byte-Regexp Bytes) (U Bytes Input-Port Path-String) Integer
(U False Integer) (U False Output-Port) Bytes #f *
(U Byte-Regexp Bytes) (U Bytes Input-Port Path-String) Integer
(U False Integer) (U False Output-Port) #f *
(U Byte-Regexp Bytes) (U Bytes Input-Port Path-String) Integer
(U False Integer) #f *
(U Byte-Regexp Bytes) (U Bytes Input-Port Path-String) Integer #f *
(U Byte-Regexp Bytes) (U Bytes Input-Port Path-String) #f *
(U Regexp String) Path-String Integer (U False Integer) (U
False Output-Port) Bytes #f *
(U Regexp String) Path-String Integer (U False Integer)
context...:
/usr/share/racket/pkgs/typed-racket-lib/typed-racket/typecheck/tc-toplevel.rkt:345:0:
type-check
/usr/share/racket/pkgs/typed-racket-lib/typed-racket/typecheck/tc-toplevel.rkt:588:0:
tc-module
/usr/share/racket/pkgs/typed-racket-lib/typed-racket/tc-setup.rkt:94:0:
tc-module/full
/usr/share/racket/pkgs/typed-racket-lib/typed-racket/typed-racket.rkt:23:4
standard-module-name-resolver
~~~
(Racket 6.10.1)
I am aware, that I do not really need the match-res, but this is only
some trying out of stuff. I am not really sure what it expects me to do
about the regexp-match. It seems it must be used differently in TR.
Should I put this in a new question ("How to use regexp-match in TR?")
instead?
On 22.04.2018 15:15, Matthew Flatt wrote:
> At Sun, 22 Apr 2018 14:54:26 +0200, Zelphir Kaltstahl wrote:
>> I am sorry, I think I am still misunderstanding it.
>>
>> When I try:
>>
>> (regexp-try-match #rx"^[1-9]+[0-9]*$" (current-input-port))
>>
>> It also results immediately in:
>>
>> #f
> Using stdin both for reading an expresion and getting input can be
> confusing. At Racket's ">" prompt, when you run
>
> > (regexp-try-match #rx"^[1-9]+[0-9]*$" (current-input-port))
>
> by hitting Return, then a newline is included is in the input stream
> just after the `(regexp-try-match ...)` expression. That newline is
> still there when you try to match against the regexp, so the match
> fails.
>
> DrRacket separates the input stream for expressions and for
> `current-input-port`. So, if you try that expression in DrRacket's
> interactions area, and if you hit the "EOF" button (to the right of the
> input box) instead of Return after a number, then you should get a
> match. Note that if you hit Return after the number, then it won't
> match even in DrRacket, because the input port will have a newline
> after the number.
>
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