It seems that everyone who learns OCaml comes away with the impression that functional programming is the New Cool Thing, and imperative programming is Bad and Must Be Avoided.
I'm going to say it now: programming fashions are stupid and counterproductive. The only things that matter are that your program is short, easy to write, easy to maintain and works correctly. How you achieve this has nothing to do with programming fads.
Reading all lines from a file is an imperative problem, and the shortest solution (easy to write, easy to maintain and correct1) uses a while loop, in OCaml or any other language:
let lines = ref [] inActually, no, I'm lying. The best solution is this:
let chan = open_in filename in
try
while true; do
lines := input_line chan :: !lines
done; []
with End_of_file ->
close_in chan;
List.rev !lines
Std.input_list chanwhich is supplied by extlib. Don't bother to duplicate functions which are already provided in commonly available libraries.
1This is only strictly speaking correct if you handle clean-up if
input_line throws some read error (exception). In the common case where you just exit the program, leaving the channel open is perfectly acceptable.
5 comments:
Actually, Python uses a for loop:
f = open('file.txt')
for line in f:
dosomethingwith(line)
f.close()
Or you can use f.readlines() if you're feeling wild and woolly.
>I'm going to say it now: programming fashions are stupid and counterproductive. The only things that matter are that your program is short, easy to write, easy to maintain and works correctly. How you achieve this has nothing to do with programming fads.
Wisest thing I've heard(read) in a while :-)
Thank you for this meaningful post [^_^]
Actually, with the patch which I hope makes its way to ExtLib, the Python extract becomes
open Enum
open IO
open File
with_file_in "file.txt" (fun f ->
iter (fun line ->
dosomething line
) (lines_of f)
)
The extract will also take care of closing the file at the end and/or in case of exception.
Oh sure, if you want to go that way...
from __future__ import with_statement
with open('file.txt') as f:
for line in f:
dosomethingwith(line)
Let's keep playing :)
With the same patch.
open Enum
open IO
open File
with_file_in "file.txt" (
lines_of |- iter do_something
)
or, if you prefer
with_file_in "file.txt" (
iter do_something -| lines_of
)
or, if you prefer
lines_of |- iter do_something |>
with_file_in "file.txt"
Although I grant you that this concision comes at the expense of readability, something which the Python version manages to avoid.
Of course, I can cheat a little further and use a nice little syntax extension of mine and end up with
with file_in "file.txt" as f
for line in lines_of f
do_something line
Which somehow reminds me of the Python version :)
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