updated README

Author: tusharad

FFI/wiki.md renamed to FFI/README.md

@@ -5,15 +5,18 @@
 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).
 
 ## How to run:
-
+```
 $ ghc ffi_examples.hs ffi_examples_c.hs
 $ ./ffi_examples
+```
 
 ## 
-You can never return char* from c function. You must create the string in heap (malloc) and then only you can return the string.
+You can never return char* from c function. You must create the string in heap (malloc) and then only you can return the string. 
 
-## Upcoming functions
+Alignment is the LCM of all the sizeof of datatypes in the strucutre/Data constructor.
+SizeOf should be the sum of all sizeof of datatypes in the structure includeing the aligment.
 
+## Upcoming functions
 1. Take 2 array...return concatenated array
 2. Take 2 pointers...return nothing
 3. take 2 strings...return one string

FFI/ffi_examples

@@ -9,6 +9,8 @@ import Foreign.ForeignPtr
 import Foreign.C.String
 import Foreign.Marshal.Array
 import System.IO.Unsafe
+import Control.Applicative ((<$>), (<*>))
+import Foreign.Storable
 
 foreign import ccall "math.h abs" c_abs :: CInt -> CInt
 foreign import ccall "math.h pow" c_pow :: CDouble -> CDouble -> CDouble
@@ -20,8 +22,57 @@ foreign import capi "printf" c_printInt :: CString -> CInt -> IO()
 foreign import ccall "intToString" c_intToString :: CInt -> CString
 foreign import ccall "bubbleSort" c_bubbleSort :: Ptr CInt -> CInt -> IO()
 foreign import ccall "toUpper" c_toUpper :: CString -> IO()
-foreign import ccall "addTwoArrays" c_addTwoArrays:: Ptr CInt -> CInt -> Ptr CInt -> Int -> IO (Ptr CInt)
-foreign import ccall "addThreeArrays" c_addThreeArrays:: Ptr CInt -> CInt -> Ptr CInt -> Int -> Ptr CInt -> Int -> IO (Ptr CInt)
+foreign import ccall "addTwoArrays" c_addTwoArrays :: Ptr CInt -> CInt -> Ptr CInt -> Int -> IO (Ptr CInt)
+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()
+
+data Student = Student {
+  roll :: Int32,
+  age :: Int32
+}
+
+data Person = Person {
+  roll2 :: Int32,
+  ch :: Char,
+  num :: Int32
+}
+
+instance Storable Student where
+  alignment _ = 4
+  sizeOf _ = 8
+  peek ptr = Student
+    <$> peekByteOff ptr 0
+    <*> peekByteOff ptr 4
+  poke ptr (Student r a) = do
+    pokeByteOff ptr 0 r
+    pokeByteOff ptr 4 a
+
+instance Storable Person where
+  alignment _ = 4
+  sizeOf _ = 12
+  peek ptr = Person
+    <$> peekByteOff ptr 0
+    <*> peekByteOff ptr 4
+    <*> peekByteOff ptr 8
+  poke ptr (Person r c n) = do
+    pokeByteOff ptr 0 r
+    pokeByteOff ptr 4 c
+    pokeByteOff ptr 8 n
+
+viewStudent :: Int -> Int -> IO ()
+viewStudent x y = do
+  let st = Student (fromIntegral x) (fromIntegral y)
+  alloca $ \ptr -> do
+    poke ptr st
+    c_viewStudent ptr
+
+viewPerson :: Int -> Char -> Int -> IO ()
+viewPerson x y z = do
+  let pt = Person (fromIntegral x) y (fromIntegral z)
+  alloca $ \ptr -> do
+    poke ptr pt
+    c_viewPerson ptr
 
 swapTwoNums :: Int -> Int -> (Int,Int)
 swapTwoNums x y = unsafePerformIO $ do
@@ -104,8 +155,11 @@ main = do
     print $ intToString 2
     -- pass int*
     bubbleSort ([4,6,3,7,1] :: [Int32])
-    -- toUpper
+    -- toUpper / pass String
     toUpper "tushar"
     -- merge array
     print $ addTwoArrays [1,2,3] [4,5,6]
     print $ addThreeArrays [1,2,3] [4,5,6] [7,8,9]
+    -- structure
+    viewStudent 2 3
+    viewPerson 2 'a' 3

FFI/ffi_examples.hs

@@ -2,6 +2,29 @@
 #include<string.h>
 #include<stdio.h>
 
+typedef struct Student{
+  int roll;
+  int age;
+}Student;
+
+typedef struct Person{
+  int roll;
+  char ch;
+  int num;
+}Person;
+
+void viewPerson(Person* p){
+  if(!p)
+    return;
+  printf("Person: %d %c %d\n",p->roll,p->ch,p->num);
+}
+
+void viewStudent(Student* st){
+  if(!st)
+    return;
+  printf("%d %d\n",st->roll,st->age);
+}
+
 void swap_nums(int* x,int* y){
     int temp = *x;
     *x = *y;

FFI/ffi_examples_c.c

@@ -1 +1,22 @@
-# haskell-examples
+# haskell-examples
+
+Haskell is statically typed, purely functional programming language. Despite being so good, One of the biggest problem, newcomers face while learning haskell is the lack tutorials/documenation. The online learning resource for haskell is quite low, compared with other languages such as Java, Python etc. Hence, I am buiilding repo, containing concept-wise examples, which will new programmers to learn the language as well as experinced haskell programmers can use this as a reference mannual.
+
+I will also try to write theory in each section's `README`.
+
+
+## Contents
+ - Foreign Functions Interface
+
+## Upcoming Material
+- Types
+- Typeclasses
+- Pattern Matching
+- Lists
+- Recursion
+- Maybe & Either
+- Maps
+- Functors
+- Applicatives
+- Monads
+- Testing