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Diffstat (limited to 'dev-haskell/enumerator/metadata.xml')
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diff --git a/dev-haskell/enumerator/metadata.xml b/dev-haskell/enumerator/metadata.xml new file mode 100644 index 000000000000..94f1cc788ba3 --- /dev/null +++ b/dev-haskell/enumerator/metadata.xml @@ -0,0 +1,44 @@ +<?xml version="1.0" encoding="UTF-8"?> +<!DOCTYPE pkgmetadata SYSTEM "http://www.gentoo.org/dtd/metadata.dtd"> +<pkgmetadata> + <herd>haskell</herd> + <longdescription> + Typical buffer&#x2013;based incremental I/O is based around a single loop, + which reads data from some source (such as a socket or file), transforms + it, and generates one or more outputs (such as a line count, HTTP + responses, or modified file). Although efficient and safe, these loops are + all single&#x2013;purpose; it is difficult or impossible to compose + buffer&#x2013;based processing loops. + + Haskell&#x2019;s concept of &#x201C;lazy I/O&#x201D; allows pure code to + operate on data from an external source. However, lazy I/O has several + shortcomings. Most notably, resources such as memory and file handles can + be retained for arbitrarily long periods of time, causing unpredictable + performance and error conditions. + + Enumerators are an efficient, predictable, and safe alternative to lazy + I/O. Discovered by Oleg Kiselyov, they allow large datasets to be processed + in near&#x2013;constant space by pure code. Although somewhat more complex + to write, using enumerators instead of lazy I/O produces more correct + programs. + + This library contains an enumerator implementation for Haskell, designed to + be both simple and efficient. Three core types are defined, along with + numerous helper functions: + + * /Iteratee/: Data sinks, analogous to left folds. Iteratees consume + a sequence of /input/ values, and generate a single /output/ value. + Many iteratees are designed to perform side effects (such as printing to + @stdout@), so they can also be used as monad transformers. + + * /Enumerator/: Data sources, which generate input sequences. Typical + enumerators read from a file handle, socket, random number generator, or + other external stream. To operate, enumerators are passed an iteratee, and + provide that iteratee with input until either the iteratee has completed its + computation, or EOF. + + * /Enumeratee/: Data transformers, which operate as both enumerators and + iteratees. Enumeratees read from an /outer/ enumerator, and provide the + transformed data to an /inner/ iteratee. + </longdescription> +</pkgmetadata> |