Code style improvement for Haskell solutions

Haskell/ProjectEuler.hs

@@ -13,7 +13,7 @@ isPrime 1 = False
 isPrime 2 = True
 isPrime 3 = True
 isPrime n =
-    n `mod` 2 /= 0 && n `mod` 3 /= 0 && null [ x | x <- candidates, n `mod` x == 0 || n `mod` (x+2) == 0 ]
+    odd n && n `mod` 3 /= 0 && null [ x | x <- candidates, n `mod` x == 0 || n `mod` (x+2) == 0 ]
     where candidates = [5,11..limit]
           limit = floor(sqrt(fromIntegral n)) + 1
 

Haskell/p001.hs

@@ -3,10 +3,10 @@
 -- Find the sum of all the multiples of 3 or 5 below 1000.
 
 sumMultiples :: Integer
-sumMultiples = sum $ filter p [ n | n <- [1..999] ]
+sumMultiples = sum $ filter p [1..999]
                 where p n = n `mod` 3 == 0 || n `mod` 5 == 0
 
 main =  do
     let result = sumMultiples
     putStrLn $ "Project Euler, Problem 1\n"
-        ++ "Answer: " ++ (show result)
+        ++ "Answer: " ++ show result

Haskell/p002.hs

@@ -15,4 +15,4 @@ sumEvenFib = sum $ filter even $ takeWhile (<=4000000) (map fib [0..])
 main =  do
     let result = sumEvenFib
     putStrLn $ "Project Euler, Problem 2\n"
-        ++ "Answer: " ++ (show result)
+        ++ "Answer: " ++ show result

Haskell/p003.hs

@@ -12,4 +12,4 @@ maxPrimeFactor n
 main = do
     let result = maxPrimeFactor 600851475143
     putStrLn $ "Project Euler, Problem 3\n"
-        ++ "Answer: " ++ (show result)
+        ++ "Answer: " ++ show result

Haskell/p004.hs

@@ -3,7 +3,7 @@
 -- Find the largest palindrome made from the product of two 3-digit numbers.
 
 isPalindrome :: Integer -> Bool
-isPalindrome n = show n == (reverse $ show n)
+isPalindrome n = show n == reverse (show n)
 
 maxPalindrome :: Integer
 maxPalindrome =
@@ -12,4 +12,4 @@ maxPalindrome =
 main = do
     let result = maxPalindrome
     putStrLn $ "Project Euler, Problem 4\n"
-        ++ "Answer: " ++ (show result)
+        ++ "Answer: " ++ show result

Haskell/p005.hs

@@ -10,4 +10,4 @@ lcmm values
 main = do
     let result = lcmm [1..20]
     putStrLn $ "Project Euler, Problem 5\n"
-        ++ "Answer: " ++ (show result)
+        ++ "Answer: " ++ show result

Haskell/p006.hs

@@ -11,9 +11,9 @@
 --Find the difference between the sum of the squares of the first one hundred natural numbers and the square of the sum.
 
 sumSquareDiff :: (Integral a) => a -> a
-sumSquareDiff n = (sum [1..n]^2) - (sum $ map (^2) [1..n])
+sumSquareDiff n = (sum [1..n]^2) - sum (map (^2) [1..n])
 
 main = do
     let result = sumSquareDiff 100
     putStrLn $ "Project Euler, Problem 6\n"
-        ++ "Answer: " ++ (show result)
+        ++ "Answer: " ++ show result

Haskell/p007.hs

@@ -10,4 +10,4 @@ nthPrime n = last $ take n [ x | x <- [1..], isPrime x ]
 main = do
     let result = nthPrime 10001
     putStrLn $ "Project Euler, Problem 7\n"
-        ++ "Answer: " ++ (show result)
+        ++ "Answer: " ++ show result

Haskell/p009.hs

@@ -17,4 +17,4 @@ prodTriplet (x, y, z) = x * y * z
 main = do
     let result = prodTriplet $ pythagoreanTriplet 1000
     putStrLn $ "Project Euler, Problem 9\n"
-        ++ "Answer: " ++ (show result)
+        ++ "Answer: " ++ show result

Haskell/p010.hs

@@ -5,9 +5,9 @@
 import ProjectEuler (isPrime)
 
 sumPrimes :: (Integral a) => a -> a
-sumPrimes n = sum [ x | x <- [1..n], isPrime(x) ]
+sumPrimes n = sum [ x | x <- [1..n], isPrime x ]
 
 main = do
     let result = sumPrimes 2000000
     putStrLn $ "Project Euler, Problem 10\n"
-        ++ "Answer: " ++ (show result)
+        ++ "Answer: " ++ show result

Haskell/p012.hs

@@ -30,4 +30,4 @@ triang500 = head [ x | x <- triangNumbers, countDivisors x > 500 ]
 main = do
     let result = triang500
     putStrLn $ "Project Euler, Problem 12\n"
-        ++ "Answer: " ++ (show result)
+        ++ "Answer: " ++ show result

Haskell/p013.hs

@@ -209,4 +209,4 @@ main = do
                                    ]
 
     putStrLn $ "Project Euler, Problem 13\n"
-        ++ "Answer: " ++ (show result)
+        ++ "Answer: " ++ show result

Haskell/p014.hs

@@ -17,8 +17,8 @@
 collatz :: (Integral a) => a -> [a]
 collatz 1 = [1]
 collatz n
-    | even n = n:(collatz $ n `div` 2)
-    | odd n  = n:(collatz $ 3 * n + 1)
+    | even n = n:collatz (n `div` 2)
+    | odd n  = n:collatz (3 * n + 1)
 
 maxCollatzLength :: Int -> Int
 maxCollatzLength n = snd $ maximum $ zip [ length (collatz x) | x <- [1..n-1] ] [1..n-1]
@@ -26,4 +26,4 @@ maxCollatzLength n = snd $ maximum $ zip [ length (collatz x) | x <- [1..n-1] ]
 main = do
     let result = maxCollatzLength 1000000
     putStrLn $ "Project Euler, Problem 14\n"
-        ++ "Answer: " ++ (show result)
+        ++ "Answer: " ++ show result

Haskell/p016.hs

@@ -7,4 +7,4 @@ import ProjectEuler (digitSum)
 main = do
     let result = digitSum $ 2 ^ 1000
     putStrLn $ "Project Euler, Problem 16\n"
-        ++ "Answer: " ++ (show result)
+        ++ "Answer: " ++ show result

Haskell/p020.hs

@@ -14,4 +14,4 @@ factorial n = n * factorial (n - 1)
 main = do
     let result = digitSum $ factorial 100
     putStrLn $ "Project Euler, Problem 20\n"
-        ++ "Answer: " ++ (show result)
+        ++ "Answer: " ++ show result

Haskell/p021.hs

@@ -12,7 +12,7 @@ properDivisors :: (Integral a) => a -> [a]
 properDivisors n = [ x | x <- [1..n-1], n `mod` x == 0]
 
 amicable :: (Integral a) => a -> a -> Bool
-amicable x y = x /= y && (sumProperDivisors x) == y && (sumProperDivisors y) == x
+amicable x y = x /= y && sumProperDivisors x == y && sumProperDivisors y == x
 
 sumAmicable :: (Integral a) => a -> a
 sumAmicable n = sum [ x | x <- [1..n-1], amicable x $ sumProperDivisors x ]
@@ -20,4 +20,4 @@ sumAmicable n = sum [ x | x <- [1..n-1], amicable x $ sumProperDivisors x ]
 main = do
     let result = sumAmicable 10000
     putStrLn $ "Project Euler, Problem 21\n"
-        ++ "Answer: " ++ (show result)
+        ++ "Answer: " ++ show result

Haskell/p023.hs

@@ -26,4 +26,4 @@ sumNotAbundant = sum $ [1..28123] \\ abundantSums
 main = do
     let result = sumNotAbundant
     putStrLn $ "Project Euler, Problem 23\n"
-        ++ "Answer: " ++ (show result)
+        ++ "Answer: " ++ show result

Haskell/p025.hs

@@ -20,11 +20,11 @@
 -- What is the index of the first term in the Fibonacci sequence to contain 1000 digits?
 
 fibs :: [Integer]
-fibs = 0:1:(zipWith (+) fibs (tail fibs))
+fibs = 0:1:zipWith (+) fibs (tail fibs)
 
-thousandDigitFib = length $ takeWhile (\x -> (length $ show x) < 1000) $ fibs
+thousandDigitFib = length $ takeWhile (\x -> length (show x) < 1000) fibs
 
 main =  do
     let result = thousandDigitFib
     putStrLn $ "Project Euler, Problem 25\n"
-        ++ "Answer: " ++ (show result)
+        ++ "Answer: " ++ show result