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Performance/IO

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Haskell Performance Resource

Constructs:
Data Types - Functions
Overloading - FFI - Arrays
Strings - Integers - I/O
Floating point - Concurrency
Modules - Monads

Techniques:
Strictness - Laziness
Avoiding space leaks
Accumulating parameter

Implementation-Specific:
GHC - nhc98 - Hugs
Yhc - JHC

Before continuing, I strongly recommend reading Performance/Strings first. Fast I/O and string handling overlap in many places, so this page will only discuss the parts that are not specific to strings.

1 Iteratee I/O

Iteratees are a relatively new approach to streaming I/O. If your code uses I/O extensively (for example, in a web server), iteratees are the best way to do it.

Using the Conduit library, a program to read a file and pipe it to stdout can be written as follows:

main = runResourceT (sourceFile "test.txt" $$ sinkHandle stdout)

2 Other solutions

If this is too high-level for you, buffer-based IO is an alternative (hGetBuf/hPutBuf). This can be particularly effective when combined with packed strings (see wc).

Some external libraries also provide memory mapped IO.

In 2006, someone came up with a solution called Streams. However, it does not seem to be maintained anymore.