From 776762298b1bcdcbeed08097f6f3b8cf1aabd27e Mon Sep 17 00:00:00 2001
From: Kiana Sheibani <kiana.a.sheibani@gmail.com>
Date: Sat, 3 Sep 2022 19:39:56 -0400
Subject: [PATCH] Create Data.Ratio

---
 ratio.ipkg         | 10 ++++++
 src/Data/Ratio.idr | 90 ++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 100 insertions(+)
 create mode 100644 ratio.ipkg
 create mode 100644 src/Data/Ratio.idr

diff --git a/ratio.ipkg b/ratio.ipkg
new file mode 100644
index 0000000..1f426b3
--- /dev/null
+++ b/ratio.ipkg
@@ -0,0 +1,10 @@
+package ratio
+version = 1.0.0
+
+authors = "Kiana Sheibani"
+license = "MIT"
+
+sourcedir = "src"
+readme = "README.md"
+
+modules = Data.Ratio
diff --git a/src/Data/Ratio.idr b/src/Data/Ratio.idr
new file mode 100644
index 0000000..63ef2a0
--- /dev/null
+++ b/src/Data/Ratio.idr
@@ -0,0 +1,90 @@
+module Data.Ratio
+
+infix 10 //
+
+export
+record Ratio a where
+  constructor MkRatio
+  nm, dn : a
+
+public export
+Rational : Type
+Rational = Ratio Integer
+
+
+gcd : (Eq a, Integral a) => a -> a -> a
+gcd x y =
+  if x == 0 then y
+  else if y == 0 then x
+  else gcd y (x `mod` y)
+
+export
+reduce : (Eq a, Integral a) => Ratio a -> Ratio a
+reduce (MkRatio n d) =
+  let g = gcd n d in MkRatio (n `div` g) (d `div` g)
+
+
+export partial
+(//) : (Eq a, Integral a) => a -> a -> Ratio a
+n // d = case d /= 0 of
+            True => reduce $ MkRatio n d
+
+
+namespace Ratio
+  export %inline
+  numer : Ratio a -> a
+  numer = nm
+
+  export %inline
+  (.numer) : Ratio a -> a
+  (.numer) = nm
+
+  export %inline
+  denom : Ratio a -> a
+  denom = dn
+
+  export %inline
+  (.denom) : Ratio a -> a
+  (.denom) = dn
+
+
+export
+Eq a => Eq (Ratio a) where
+  MkRatio n d == MkRatio m b = n == m && d == b
+
+export
+(Ord a, Num a) => Ord (Ratio a) where
+  compare (MkRatio n d) (MkRatio m b) =
+    flipIfNeg (b*d) $ compare (n*b) (m*d)
+    where
+      flipIfNeg : a -> Ordering -> Ordering
+      flipIfNeg x EQ = EQ
+      flipIfNeg x LT = if x >= 0 then LT else GT
+      flipIfNeg x GT = if x >= 0 then GT else LT
+
+export
+Show a => Show (Ratio a) where
+  showPrec p (MkRatio n d) =
+    let p' = User 10
+    in  showParens (p >= p') (showPrec p' n ++ " // " ++ showPrec p' d)
+
+export
+(Eq a, Integral a) => Num (Ratio a) where
+  MkRatio n d + MkRatio m b = reduce $ MkRatio (n*b + m*d) (d*b)
+  MkRatio n d * MkRatio m b = reduce $ MkRatio (n*m) (d*b)
+  fromInteger x = MkRatio (fromInteger x) 1
+
+export
+(Eq a, Integral a, Neg a) => Neg (Ratio a) where
+  negate (MkRatio n d) = MkRatio (-n) d
+  MkRatio n d - MkRatio m b = reduce $ MkRatio (n*b - m*d) (d*b)
+
+export
+(Eq a, Integral a, Abs a) => Abs (Ratio a) where
+  abs (MkRatio n d) = MkRatio (abs n) (abs d)
+
+export
+(Eq a, Integral a) => Fractional (Ratio a) where
+  recip (MkRatio n d) = case n /= 0 of True => MkRatio d n
+  MkRatio n d / MkRatio m b = case m /= 0 of
+    True => reduce $ MkRatio (n*b) (m*d)