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

[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.

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[George Neuner]

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

[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).