From 05f89b991dfeaf87ff274e55ab095b4409addf3c Mon Sep 17 00:00:00 2001
From: Mahdi Dibaiee <mdibaiee@aol.com>
Date: Fri, 4 Nov 2016 22:32:19 +0330
Subject: [PATCH] fix: negation on negative number

---
 src/Data/MathExpr.hs | 1 +
 1 file changed, 1 insertion(+)

diff --git a/src/Data/MathExpr.hs b/src/Data/MathExpr.hs
index 99f061a..84ddaf5 100644
--- a/src/Data/MathExpr.hs
+++ b/src/Data/MathExpr.hs
@@ -81,6 +81,7 @@ module Data.MathExpr
           -- negative numbers come in the form ["num", "-"]
           helper [] [o] = read o
           helper [n, "-"] [] = negate . read $ n
+          helper ["-"] [n] = negate . read $ n
           helper (c:cs) os
             | c == "-" && length os < 2 =
                 let result :: Double = negate . read . head $ cs