feat(third_party/bazel): Check in rules_haskell from Tweag

third_party/bazel/rules_haskell/examples/README.md

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+# rule_haskell examples
+
+Examples of using [rules_haskell][rules_haskell], the Bazel rule set
+for building Haskell code.
+
+* [**vector:**](./vector/) shows how to build the `vector` package as
+  found on Hackage, using a Nix provided compiler toolchain.
+* [**rts:**](./rts/) demonstrates foreign exports and shows how to
+  link against GHC's RTS library, i.e. `libHSrts.so`.
+  
+## **Important**
+
+Run all commands from the root of `rules_haskell`.
+If you `cd examples/`, bazel *will* [break on
+you](https://github.com/tweag/rules_haskell/issues/740).
+This is a current problem with bazel workspaces.
+
+## Root Workspace
+
+Build everything in the root workspace with;
+
+```
+$ bazel build @io_tweag_rules_haskell_examples//...
+```
+
+Show every target of the vector example;
+
+```
+$ bazel query @io_tweag_rules_haskell_examples//vector/...
+@io_tweag_rules_haskell_examples//vector:vector
+@io_tweag_rules_haskell_examples//vector:semigroups
+@io_tweag_rules_haskell_examples//vector:primitive
+@io_tweag_rules_haskell_examples//vector:ghc-prim
+@io_tweag_rules_haskell_examples//vector:deepseq
+@io_tweag_rules_haskell_examples//vector:base
+```
+
+Build the two main Haskell targets;
+
+```
+$ bazel build @io_tweag_rules_haskell_examples//vector
+$ bazel build @io_tweag_rules_haskell_examples//rts:add-one-hs
+```
+
+[rules_haskell]: https://github.com/tweag/rules_haskell