Readme for hls-graph

Author: pepeiborra

hls-graph/README.md

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+# hls-graph - a limited reimplementation of Shake for in-memory build graphs
+
+`ghcide` was originally built on top of [Shake](http://shakebuild.com), a Haskell build system. Nowadays Shake has been replaced by a special purpose implementation of a build graph called hls-graph, which drops all the persistency features in exchange for simplicity and performance.
+
+Features:
+
+* Dynamic dependencies
+* User defined rules (there are no predefined File rules as in Shake)
+* Build reports (a la Shake profiling)
+* "Reactive" change tracking for minimal rebuilds (not available in Shake)
+
+What's missing:
+
+* Persistence
+* A default set of rules for file system builds
+* A testsuite
+* General purpose application - many design decisions make assumptions specific to ghcide