From: Francis Russell <francis@unchartedbackwaters.co.uk>
Date: Fri, 12 Apr 2013 16:10:17 +0000 (+0100)
Subject: Fix raising rationals to negative integers.
X-Git-Url: https://git.unchartedbackwaters.co.uk/w/?a=commitdiff_plain;h=0251b0b84648864af5e9b82c58eef093aa647945;p=francis%2Flta.git

Fix raising rationals to negative integers.

Haskell's Ratio implementation complains about negative exponents.
---

diff --git a/LTA/Symbolic.hs b/LTA/Symbolic.hs
index 3472fcb..c0e04d0 100644
--- a/LTA/Symbolic.hs
+++ b/LTA/Symbolic.hs
@@ -10,7 +10,7 @@ module LTA.Symbolic
   ) where
 
 import Control.Applicative ((<$>))
-import Data.Ratio (numerator, denominator, (%))
+import Data.Ratio (numerator, denominator)
 import Data.List (foldl')
 import Data.Map (Map)
 import qualified Data.Map as Map
@@ -150,7 +150,9 @@ evalPow (Literal a) (Literal b) = evalPow' a b where
   evalPow' (FloatLiteral x) (FloatLiteral y) = Just . FloatLiteral $ x ** y
   evalPow' (RationalLiteral x) (RationalLiteral y) = if (denominator y) == 1
     then let power = numerator y in
-      Just . RationalLiteral $ (numerator x ^ power) % (denominator x ^ power)
+     Just . RationalLiteral $ if power >= 0
+       then x ^ power
+       else (recip x) ^ (- power)
     else Nothing
   evalPow' _ _ = Nothing
 evalPow _ _ = Nothing