Re: newline comparison?

[Matthew Flatt <mflatt@cs.utah.edu>]

Quoting Chris Uzdavinis:
> Here's the situation: I have a string whose value is a single newline
> character.  (The variable name is 'line'.)  I want to ask in a
> (cond...) statement the question "is this string equal to the string
> containing just a newline?"
> 
> [...]
>
>         ([string=? line "\n"]  (do-something)))

What would work in version 199.X (the upcoming release, available only
through CVS), but not 103.X.

>         ([equal? (string-ref line 0) #\newline]
>         ([eq? string-ref line 0) #\newline]  (do-something)))

Those should work.

But I think the problem may be here:

>   (let ([line (read-line input)]) ;; assume this reads in a newline only

`read-line' strips off the newline character, so a line containing
nothing will produce the empty string.

Beware of variying newline conventions. For example, when reading a
DOS/Windows file, you'll get both #\newline and #\return from the port
(and `read-line' will return the #\return characters) unless it's opened
in 'text mode.

Matthew