Re: [racket-users] reading s-expressions from a file

[gfb]

Shouldn't the for be (for ([expr (in-producer read eof)] ⋯). One could also 
specify the input port there, as shown in reference for in-producer 

 
, possibly inside call-with-input-file (although that vs 
with-input-from-file is probably a matter of taste).

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Re: [racket-users] reading s-expressions from a file

[George Neuner]

On 7/17/2020 8:19 PM, Hendrik Boom wrote:

Yes,  I know the functino for reading s-expressions seems to be (read [in]).

I want a loop that reads S-expressions and does something to each one, until 
there are no more to be found in a file.

Now of course that's absurdly easy to do with a tail-recursice loop.

But I's like it to look like a loop, with (for ...) or (while ...) or
(loop ...) or something like that.

But I fail to fine any iterators that process a file, such as (in-file
...)

There's a long list of iterators in
https://docs.racket-lang.org/reference/for.html
and in
https://docs.racket-lang.org/guide/for.html

An I just looking in the wrong place, or are there really no iterators
for reading a stream of s-expressions from a file.

-- hendrik


This should work if you're reading the sexprs for value:

(with-input-from-file /filename/
  (lambda ()
    (for [(expr (read))]
  :
    )))

If your intent is to read/parse the sexprs as text, there isn't a simple 
way to do that.  Regex is problematic for nested expressions ... you 
could try "read-syntax" if you are familiar with macros, or "match" if 
you know what patterns to look for.


There's no "in-match" sequence, so if you want a loop that *appears* 
simple [match in the /"for-clause"/], you'll have to write some glue: a 
helper that returns one match result at a time so as to plug nicely into 
a loop.


George

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Re: [racket-users] reading s-expressions from a file

[Sorawee Porncharoenwase]

(with-input-from-file "abc" (thunk (sequence->list (in-port

Note that you need to “read” in the dynamic extent of with-input-from-file.
Outside it, the port is closed.

On Fri, Jul 17, 2020 at 5:19 PM Hendrik Boom  wrote:

> Yes,  I know the functino for reading s-expressions seems to be (read
> [in]).
>
> I want a loop that reads S-expressions and does something to each one,
> until there are no more to be found in a file.
>
> Now of course that's absurdly easy to do with a tail-recursice loop.
>
> But I's like it to look like a loop, with (for ...) or (while ...) or
> (loop ...) or something like that.
>
> But I fail to fine any iterators that process a file, such as (in-file
> ...)
>
> There's a long list of iterators in
>https://docs.racket-lang.org/reference/for.html
> and in
>https://docs.racket-lang.org/guide/for.html
>
> An I just looking in the wrong place, or are there really no iterators
> for reading a stream of s-expressions from a file.
>
> -- hendrik
>
> --
> 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.
> To view this discussion on the web visit
> https://groups.google.com/d/msgid/racket-users/20200718001905.elzyuu42gje45j7t%40topoi.pooq.com
> .
>

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[racket-users] reading s-expressions from a file

[Hendrik Boom]

Yes,  I know the functino for reading s-expressions seems to be (read [in]).

I want a loop that reads S-expressions and does something to each one, until 
there are no more to be found in a file.

Now of course that's absurdly easy to do with a tail-recursice loop.

But I's like it to look like a loop, with (for ...) or (while ...) or 
(loop ...) or something like that.

But I fail to fine any iterators that process a file, such as (in-file 
...)

There's a long list of iterators in 
   https://docs.racket-lang.org/reference/for.html
and in 
   https://docs.racket-lang.org/guide/for.html

An I just looking in the wrong place, or are there really no iterators 
for reading a stream of s-expressions from a file.

-- hendrik

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