simple-enumeration 0.2 → 0.2.1

raw patch · 4 files changed

+34/−5 lines, 4 files

Files

• ChangeLog.md +4/−0
• README.md +2/−0
• simple-enumeration.cabal +1/−1
• src/Data/Enumeration/Invertible.hs +27/−4

@@ -1,5 +1,9 @@ # Changelog for enumeration +## 0.2.1 (25 June 2020)++[Make `Data.Enumeration.Invertible.functionOf` a bit more permissive.](https://github.com/byorgey/enumeration/commit/59090f46ce01d7eda7371ba673fe54763b96c97e)+ ## 0.2 (3 July 2019)  Added `Data.Enumeration.Invertible`.

@@ -1,3 +1,5 @@+![CI](https://github.com/byorgey/enumeration/workflows/CI/badge.svg)+ # Lightweight, efficiently indexable enumerations  This package defines a type of *enumerations*, along with combinators

@@ -1,7 +1,7 @@ cabal-version: 1.12  name:           simple-enumeration-version:        0.2+version:        0.2.1 synopsis:       Finite or countably infinite sequences of values. description:    Finite or countably infinite sequences of values,                 supporting efficient indexing and random sampling.

@@ -646,7 +646,12 @@ -- | @functionOf a b@ creates an enumeration of all functions taking --   values from the enumeration @a@ and returning values from the --   enumeration @b@.  As a precondition, @a@ must be finite;---   otherwise @functionOf@ throws an error.+--   otherwise @functionOf@ throws an error. There are two exceptions:+--   first, if @b@ has cardinality 1, we get an enumeration of exactly+--   one function which constantly returns the one element of @b@,+--   even if @a@ is infinite.  Second, if @b@ has cardinality 0, we+--   get a singleton enumeration if @a@ also has cardinality 0, and an+--   empty enumeration otherwise (even if @a@ is infinite). -- -- >>> bbs = functionOf (boundedEnum @Bool) (boundedEnum @Bool) -- >>> card bbs@@ -658,10 +663,28 @@ -- -- >>> locate (functionOf bbs (boundedEnum @Bool)) (\f -> f True) -- 5+--+-- >>> n2u = functionOf nat unit+-- >>> card n2u+-- Finite 1+-- >>> (select n2u 0) 57+-- ()+--+-- >>> n2o = functionOf nat void+-- >>> card n2o+-- Finite 0+-- >>> o2o = functionOf void void+-- >>> card o2o+-- Finite 1 functionOf :: IEnumeration a -> IEnumeration b -> IEnumeration (a -> b)-functionOf as bs = case card as of-  Infinite -> error "functionOf with infinite domain"-  Finite n -> mapE toFunc fromFunc (finiteEnumerationOf (fromIntegral n) bs)+functionOf as bs = case card bs of+  Finite 1 -> singleton (\_ -> select bs 0)   -- 1^x = 1+  Finite 0 -> case card as of                 -- 0^0 = 1, 0^x = 0+    Finite 0 -> singleton (\_ -> error "called function with empty domain")+    _        -> void+  _        -> case card as of+    Infinite -> error "functionOf with infinite domain"+    Finite n -> mapE toFunc fromFunc (finiteEnumerationOf (fromIntegral n) bs)    where     toFunc bTuple a = E.select bTuple (locate as a)