Add simple spreadsheet example

README.md

@@ -1,3 +1,106 @@
-# rock
+# rock [![Hackage](https://img.shields.io/hackage/v/rock.svg)](https://hackage.haskell.org/package/rock)
 
-A build system inspired by _Build systems à la carte_ and Haxl.
+A build system inspired by [Build systems à la carte](https://www.microsoft.com/en-us/research/publication/build-systems-la-carte/) and [Haxl](http://hackage.haskell.org/package/haxl).
+
+Used in [Sixten](https://github.com/ollef/sixten) and
+[Sixty](https://github.com/ollef/sixty) to achieve incremental and query driven
+compiler architectures.
+
+# Example
+
+```haskell
+{-# language GADTs #-}
+{-# language NoImplicitPrelude #-}
+{-# language OverloadedStrings #-}
+{-# language StandaloneDeriving #-}
+{-# language TemplateHaskell #-}
+
+import Protolude
+
+import Data.GADT.Compare.TH (deriveGEq, deriveGCompare)
+import qualified Rock
+
+data Query a where
+  A :: Query Integer
+  B :: Query Integer
+  C :: Query Integer
+  D :: Query Integer
+
+deriving instance Show (Query a)
+
+deriveGEq ''Query
+deriveGCompare ''Query
+
+rules :: Rock.Rules Query
+rules key = do
+  putText $ "Fetching " <> show key
+  case key of
+    A -> pure 10
+    B -> do
+      a <- Rock.fetch A
+      pure $ a + 20
+    C -> do
+      a <- Rock.fetch A
+      pure $ a + 30
+    D ->
+      (+) <$> Rock.fetch B <*> Rock.fetch C
+
+main :: IO ()
+main = do
+  do
+    putText "Running"
+    result <- Rock.runTask Rock.sequentially rules (Rock.fetch D)
+    print result
+  do
+    putText "Running with memoisation"
+    memoVar <- newMVar mempty
+    result <-
+      Rock.runTask
+        Rock.sequentially
+        (Rock.memoise memoVar rules)
+        (Rock.fetch D)
+    print result
+  do
+    putText "Running with memoisation using the parallel strategy"
+    memoVar <- newMVar mempty
+    result <-
+      Rock.runTask
+        Rock.inParallel
+        (Rock.memoise memoVar rules)
+        (Rock.fetch D)
+    print result
+```
+
+Prints
+
+```
+Running
+Fetching D
+Fetching B
+Fetching A
+Fetching C
+Fetching A
+70
+Running with memoisation
+Fetching D
+Fetching B
+Fetching A
+Fetching C
+70
+Running with memoisation using the parallel strategy
+Fetching D
+Fetching C
+Fetching B
+Fetching A
+70
+```
+
+# Related projects
+
+* [Shake](http://hackage.haskell.org/package/shake)
+* [Salsa](https://crates.io/crates/salsa)
+
+# Contributions
+
+... are very welcome, especially in the areas of documentation, examples,
+testing, and benchmarking.

examples/Spreadsheet.hs

@@ -0,0 +1,60 @@
+{-# language GADTs #-}
+{-# language NoImplicitPrelude #-}
+{-# language OverloadedStrings #-}
+{-# language StandaloneDeriving #-}
+{-# language TemplateHaskell #-}
+
+import Protolude
+
+import Data.GADT.Compare.TH (deriveGEq, deriveGCompare)
+import qualified Rock
+
+data Query a where
+  A :: Query Integer
+  B :: Query Integer
+  C :: Query Integer
+  D :: Query Integer
+
+deriving instance Show (Query a)
+
+deriveGEq ''Query
+deriveGCompare ''Query
+
+rules :: Rock.Rules Query
+rules key = do
+  putText $ "Fetching " <> show key
+  case key of
+    A -> pure 10
+    B -> do
+      a <- Rock.fetch A
+      pure $ a + 20
+    C -> do
+      a <- Rock.fetch A
+      pure $ a + 30
+    D ->
+      (+) <$> Rock.fetch B <*> Rock.fetch C
+
+main :: IO ()
+main = do
+  do
+    putText "Running"
+    result <- Rock.runTask Rock.sequentially rules (Rock.fetch D)
+    print result
+  do
+    putText "Running with memoisation"
+    memoVar <- newMVar mempty
+    result <-
+      Rock.runTask
+        Rock.sequentially
+        (Rock.memoise memoVar rules)
+        (Rock.fetch D)
+    print result
+  do
+    putText "Running with memoisation using the parallel strategy"
+    memoVar <- newMVar mempty
+    result <-
+      Rock.runTask
+        Rock.inParallel
+        (Rock.memoise memoVar rules)
+        (Rock.fetch D)
+    print result

rock.cabal

@@ -30,7 +30,6 @@ library
   exposed-modules:
                        Rock
                        Rock.Core
-                       Rock.Examples
                        Rock.HashTag
                        Rock.Hashed
                        Rock.Traces
@@ -47,3 +46,18 @@ library
 source-repository head
   type:     git
   location: https://github.com/ollef/rock
+
+flag examples
+  Description: "Build examples"
+  Default:     False
+  Manual:      True
+
+executable rock-spreadsheet
+  if !flag(examples)
+    buildable:         False
+  main-is:             Spreadsheet.hs
+  ghc-options:         -Wall
+                       -threaded
+  hs-source-dirs:      examples
+  default-language:    Haskell2010
+  build-depends:       base, rock, protolude, dependent-sum-template