CODEWITHSUNDEEP
memory-managementhaskellprofiling
Fopa Léon Constantin
Fopa Léon Constantin

Reputation: 12363

How to go from String to Data.ByteString.Lazy in an existing Haskell code?

I have a Haskell code which use a lot of String, while profilling it, it appear that the code use a lot of memory to store Lists []. One solution to this problem is to use Data.ByteString.Lazy instead of String, but

what I have to care about while doing this ?,

which part of the code have to be look carefully : fold, map, ... ?

thanks for reply

Upvotes: 4

Views: 1359

Answers (2)

fuz
fuz

Reputation: 92986

You should know, that a ByteString is really bad for things like iteration over it elements, but better for Concatation, etc.

If you want to work with ByteStrings, you have to convert the String to a ByteString, just do something like

import Data.ByteString.Lazy as B

and stick a B in front of each function which works with them - most functions for String also exists for ByteString. Please notice - you have to convert the Strings you use to a ByteString with some functions.

If you use Data.ByteString.Lazy.Char8 instead, you can easily use pack, but all chars greater than 255 will be truncated. Also, this type is more suitable for binary data and safes memory.

Edit: You should consider using the package text, if you want to work on text-strings. Look here for further details.

Upvotes: 2

Travis Brown
Travis Brown

Reputation: 139038

The OverloadedStrings extension can be handy if you're using GHC and are converting code with a lot of string literals. Just add the following to the top of your source file:

{-# LANGUAGE OverloadedStrings #-}

And you don't have to use B.pack on any string literals in your code. You could have the following, for example:

equalsTest :: B.ByteString -> Bool
equalsTest x = x == "Test"

Without the extension this would give an error, since you can't use == on a ByteString and a [Char]. With the extension, string literals have type (IsString a) => a, and ByteString is an instance of IsString, so "Test" here is typed as a ByteString and there's no error.

Upvotes: 5

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