Enable 'in' instruction handler

README.md

@@ -30,6 +30,7 @@ List of available instructions:
 | ``0x18`` | ``CLR x``  | Wipe out ``x`` values before the top value from the stack                      |
 
 ## Example
+### Example 1
 The `2*3+5` formula written as the MVM assembly code:
 ```asm
 main: push 2
@@ -41,15 +42,15 @@ main: push 2
       clr 2
       halt
 
-sum: ld 0
-     ld 1
-     add
-     ret
+sum:  ld 0
+      ld 1
+      add
+      ret
 
-prd: ld 0
-     ld 1
-     mul
-     ret
+prd:  ld 0
+      ld 1
+      mul
+      ret
 ```
 The result of execution with the `debug = True` flag:
 ```
@@ -90,4 +91,23 @@ VM {_pc = 14, _fp = -1, _stack = fromList [11], _halt = False, _debug = True}
 Done:
 VM {_pc = 14, _fp = -1, _stack = fromList [11], _halt = True, _debug = True}
 
+```
+### Example 2
+The base I/O example - simple echo:
+```asm
+read:  in
+       dup
+       out
+       push 0x0A
+       sub       
+       jne &read ; loop until the input != new line (0x0A)
+       halt
+```
+The execution for the input string `Hello, world!`:
+```
+Hello, world!
+
+
+Done:
+VM {_pc = 8, _fp = -1, _stack = fromList [], _halt = True, _debug = False}
 ```

app/VirtualMachine/Instruction.hs

@@ -1,7 +1,8 @@
 module VirtualMachine.Instruction where
 
-import Data.Char (chr)
+import Data.Char (chr, ord)
 import Data.Word (Word8)
+import System.IO (stdin, hGetChar)
 import Control.Monad.Except (throwError)
 import Control.Monad.Trans (lift, liftIO)
 import Control.Monad.Trans.Except (ExceptT, except)
@@ -49,7 +50,7 @@ instructions = [ Simple  { _op = Nop,  _noParams = 0, _noPops = 0, _sAction = (\
                , Complex { _op = Jge,  _noParams = 1, _noPops = 1, _cAction = jumpIf (>=)                                          }
                , Complex { _op = Jle,  _noParams = 1, _noPops = 1, _cAction = jumpIf (<=)                                          }
                , Complex { _op = Ld,   _noParams = 1, _noPops = 0, _cAction = load                                                 }
-               , Complex { _op = In,   _noParams = 0, _noPops = 0, _cAction = niy In                                               }
+               , Complex { _op = In,   _noParams = 0, _noPops = 0, _cAction = input                                                }
                , Complex { _op = Out,  _noParams = 0, _noPops = 1, _cAction = output                                               }
                , Complex { _op = Clr,  _noParams = 1, _noPops = 0, _cAction = clear                                                }
                ]
@@ -112,6 +113,13 @@ jumpIf p (addr:_) (top:_) = lift $ do
 jumpIf _ [] _  = throwError "Address expected"
 jumpIf _ _  [] = throwError "Empty stack - nothing to compare"  
 
+input :: Params -> Pops -> ExceptT String Machine ()
+input _ _ = lift $ do
+  c <- liftIO $ hGetChar stdin
+  push [ord c]
+  forward 1
+  return()
+
 output :: Params -> Pops -> ExceptT String Machine ()
 output _ (char:_) = lift $ do
   liftIO $ putStr $ [chr char]
@@ -119,7 +127,6 @@ output _ (char:_) = lift $ do
   return ()
 output _ [] = except $ Left $ "Empty stack - nothing to output"
 
-
 load :: Params -> Pops -> ExceptT String Machine ()
 load (index:_) _ = do
   fp <- lift getFp