feat: even and odd for Nat and Integral (#3021)

CHANGELOG.md

@@ -175,6 +175,7 @@
 
 * Adds `leftmost` and `rightmost` to `Control.Order`, a generalisation of `min` and `max`.
 
+* Adds `even` and `odd` to `Data.Integral`.
 * `Eq` and `Ord` implementations for `Fin n` now run in constant time.
 
 * Adds `getTermCols` and `getTermLines` to the base library. They return the

libs/base/Data/Integral.idr

@@ -0,0 +1,9 @@
+module Data.Integral
+
+export
+even : Integral n => Eq n => n -> Bool
+even n = n `mod` 2 == 0
+
+export
+odd : Integral n => Eq n => n -> Bool
+odd = not . even

tests/base/data_integral/Integral.idr

@@ -0,0 +1,52 @@
+import Data.Integral
+
+Cases : Type
+Cases = List Bool
+
+natEvenCases : Cases
+natEvenCases = [
+    even 0,
+    even 2,
+    even 4,
+    even Z,
+    even (S (S Z))
+  ]
+
+natOddCases : Cases
+natOddCases = [
+    odd 1,
+    odd 3,
+    odd 5,
+    odd (S Z),
+    odd (S (S (S Z)))
+  ]
+
+integralEvenCases : Cases
+integralEvenCases = [
+    even (-4),
+    even (-2),
+    even 0,
+    even 2,
+    even 4
+]
+
+integralOddCases : Cases
+integralOddCases = [
+    odd (-5),
+    odd (-3),
+    odd (-1),
+    odd 1,
+    odd 3,
+    odd 5
+]
+
+main : IO ()
+main = do
+  printLn "Nat Even"
+  printLn natEvenCases
+  printLn "Nat Odd"
+  printLn natOddCases
+  printLn "Integral Even"
+  printLn integralEvenCases
+  printLn "Integral Odd"
+  printLn integralOddCases

tests/base/data_integral/expected

@@ -0,0 +1,10 @@
+1/1: Building Integral (Integral.idr)
+Main> "Nat Even"
+[True, True, True, True, True]
+"Nat Odd"
+[True, True, True, True, True]
+"Integral Even"
+[True, True, True, True, True]
+"Integral Odd"
+[True, True, True, True, True, True]
+Main> Bye for now!

tests/base/data_integral/input

@@ -0,0 +1,2 @@
+:exec main
+:q

tests/base/data_integral/run

@@ -0,0 +1,3 @@
+rm -rf build
+
+$1 --no-color --console-width 0 --no-banner Integral.idr < input