Few FFI examples, Readme, BinarySearch

Author: tusharad

.gitignore

@@ -1,2 +1,3 @@
 *.o
 *.hi
+*.exe

FFI/README.md

@@ -1,6 +1,8 @@
-[https://ghc.gitlab.haskell.org/ghc/doc/users_guide/exts/ffi.html]
-[https://en.wikibooks.org/wiki/Haskell/FFI]
-[https://wiki.haskell.org/Foreign_Function_Interface]
+[resource1](https://ghc.gitlab.haskell.org/ghc/doc/users_guide/exts/ffi.html)
+
+[resource2](https://en.wikibooks.org/wiki/Haskell/FFI)
+
+[resource3](https://wiki.haskell.org/Foreign_Function_Interface)
 
 Haskell FFI (Foreign Function Interface) helps calling c functions from haskell and vice versa. You just need to write function signature with appropriate data types (haskell equivalent data types of c).
 

FFI/ffi_examples.hs

@@ -26,6 +26,7 @@ foreign import ccall "addTwoArrays" c_addTwoArrays :: Ptr CInt -> CInt -> Ptr CI
 foreign import ccall "addThreeArrays" c_addThreeArrays :: Ptr CInt -> CInt -> Ptr CInt -> Int -> Ptr CInt -> Int -> IO (Ptr CInt)
 foreign import ccall "viewStudent" c_viewStudent :: Ptr Student -> IO()
 foreign import ccall "viewPerson" c_viewPerson :: Ptr Person -> IO()
+foreign import ccall "getStudent" c_getStudent :: CInt -> CInt -> IO(Ptr Student)
 
 data Student = Student {
   roll :: Int32,
@@ -47,6 +48,9 @@ instance Storable Student where
   poke ptr (Student r a) = do
     pokeByteOff ptr 0 r
     pokeByteOff ptr 4 a
+instance Show Student where
+    show st = "Roll number: " ++ show (roll st) ++ " Age: " ++ show (age st)
+
 
 instance Storable Person where
   alignment _ = 4
@@ -67,6 +71,13 @@ viewStudent x y = do
     poke ptr st
     c_viewStudent ptr
 
+getStudent :: Int -> Int -> IO ()
+getStudent r a = do
+  let stPtr = unsafePerformIO $ c_getStudent (fromIntegral r) (fromIntegral a)
+  foreignPtr <- newForeignPtr p_free stPtr
+  st <- withForeignPtr foreignPtr $ \ptr -> peek ptr
+  print st
+
 viewPerson :: Int -> Char -> Int -> IO ()
 viewPerson x y z = do
   let pt = Person (fromIntegral x) y (fromIntegral z)
@@ -163,3 +174,5 @@ main = do
     -- structure
     viewStudent 2 3
     viewPerson 2 'a' 3
+    getStudent 2 3
+    

FFI/ffi_examples_c.c

@@ -25,6 +25,13 @@ void viewStudent(Student* st){
   printf("%d %d\n",st->roll,st->age);
 }
 
+Student* getStudent(int roll,int age){
+  Student* st = malloc(sizeof(struct Student*));
+  st->roll = roll;
+  st->age = age;
+  return st;
+}
+
 void swap_nums(int* x,int* y){
     int temp = *x;
     *x = *y;

Recursion/BinarySearch.hs

@@ -0,0 +1,14 @@
+module BinarySearch where
+import Data.Int
+
+binarySearch_ :: [Int32] -> Int32 -> Int -> Int -> Maybe Int
+binarySearch_ list1 elem low high
+    | low >= high = Nothing
+    | (list1 !! mid) < elem = binarySearch_ list1 elem (mid+1) high
+    | (list1 !! mid) > elem = binarySearch_ list1 elem low (mid-1)
+    | otherwise = Just mid
+    where 
+        mid = low + ((high-low) `div` 2)
+
+binarySearch :: [Int32] -> Int32 -> Maybe Int
+binarySearch list1 elem = binarySearch_ list1 elem 0 (length list1)

Recursion/Fibonacci.hs

@@ -0,0 +1 @@
+module Fibonacci where

Recursion/Main.hs

@@ -0,0 +1,8 @@
+module Main where
+import BinarySearch
+
+main :: IO()
+main = do
+    let list1 = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11]
+    let elem = 7
+    print $ binarySearch list1 elem 

Recursion/README.md

@@ -0,0 +1,5 @@
+[Resource1](http://www.jacobsheehy.com/2009/03/binary-search-in-haskell/)
+
+Recursion is a crucial part of haskell. I sure you already what recursion is...
+
+In the examples, I have used lists, but for performance improvements you can use [Arrays](https://hackage.haskell.org/package/array-0.5.6.0/docs/Data-Array.html).