| <?xml version="1.0" encoding="UTF-8"?> |
| <!DOCTYPE pkgmetadata SYSTEM "http://www.gentoo.org/dtd/metadata.dtd"> |
| <pkgmetadata> |
| <maintainer type="project"> |
| <email>haskell@gentoo.org</email> |
| <name>Gentoo Haskell</name> |
| </maintainer> |
| <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> |