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 Syntax Quickref: Turing <--> Haskell
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wtd




PostPosted: Thu Mar 03, 2005 7:42 pm   Post subject: Syntax Quickref: Turing <--> Haskell

Haskell for the Turing Programmer

Input-Output

Printing to the standard output.

Turing
code:
put "Hello"


Haskell
code:
putStrLn "Hello"


The same, without skipping to a newline.

Turing
code:
put "Hello" ..


Haskell
code:
do putStr "Hello"
   hFlush stdout


Printing an integer.

Turing
code:
put 42


Haskell
code:
putStrLn (show 42)


Printing a floating point number.

Turing
code:
put 42.3


Haskell
code:
putStrLn (show 42.3)


Getting a line from the keyboard.

Turing
code:
var line : string
get line : *


Haskell
code:
line :: IO String
line = getLine


Getting a single character from the keyboard.

Turing
code:
var ch : string
get ch : 1


Haskell
code:
ch :: IO Char
ch = getChar


Getting an integer from the keyboard.

Turing
code:
var i : int
get i


Haskell
code:
readInt :: String -> Int
readInt str = case reads str of
  []      -> 0
  [(n,_)] -> n
  _       -> error "I said an int, you insolent hacker!"
 
f :: IO Int 
f = do l <- getLine
       return (readFloat l)


Getting a float from the keyboard.

Turing
code:
var f : real
get f


Haskell
code:
readFloat :: String -> Float
readFloat str = case reads str of
  []      -> 0
  [(n,_)] -> n
  _       -> error "I said a float, you insolent hacker!"
 
f :: IO Float 
f = do l <- getLine
       return (readFloat l)


Math

code:
Turing    | Haskell     | Result
----------+-------------+---------
 4 + 3    |  4 + 3      |  7
 4 - 2    |  4 - 2      |  2
 2 * 3    |  2 * 3      |  6
 2 / 5    |  2 / 5      |  0.4
 6 div 4  |  div 6 4    |  1
          |  6 `div` 4  |
 6 rem 4  |  mod 6 4    |  2
          |  6 `mod` 4  |
 3 ** 2   |  3 ** 2     |  9.0
          |  3 ^ 2      |
          |  3 ^^ 2     |
 sin      |  sin        |
 cos      |  cos        |
          |  tan        |
          |  asin       |
          |  acos       |
          |  atan       |


Comparisons

code:
Turing  | Haskell     
--------+----------
 =      |  ==     
 not=   |  /=     
 <, <=  |  <, <=     
 >, >=  |  >, >=     
 not    |  not   
 and    |  &&
 or     |  ||


Conditional Statements/Expressions

code:
Turing                      | Haskell     
----------------------------+------------------------------
 if condition then          |  if condition
   statement1               |    then expression1
 elsif otherCondition then  |    else if otherCondition
   statement2               |      then expression2
 else                       |      else defaultExpression
   defaultStatement         |
 end if                     |
----------------------------+------------------------------
 case value of              |  case value of
   label 1: statement1      |    1 -> expression1
   label 2: statement2      |    2 -> expression2
   label: default           |    _ -> default
 end case                   |


Function Definition

code:
Turing                              | Haskell     
------------------------------------+--------------------------------------------
 function fooBar : string           |  fooBar :: String
   result "foo, bar"                |  fooBar = "foo, bar"
 end fooBar                         |   
------------------------------------+--------------------------------------------
 function square (n : int) : float  |  square :: Int -> Float
   result n ** 2                    |  square n = n ** 2
 end square                         |  or:
                                    |  square = (** 2)
------------------------------------+--------------------------------------------
 procedure greet (name : string)    |  greet :: String -> IO ()
   put "Hello, " + name             |  greet name = putStrLn ("Hello, " ++ name)
 end greet                          |  or:
                                    |  greet = putStrLn . ("Hello, " ++) 
------------------------------------+--------------------------------------------
 procedure greet (name : string)    |  greet :: String -> IO ()
   var greeting := "Hello, " + name |  greet name = let greeting = "Hello, " ++ name in
   put greeting                     |    putStrLn greeting
 end greet                          |  or:
                                    |  greet name = putStrLn greeting
                                    |    where
                                    |      greeting = "Hello, " ++ name
------------------------------------+--------------------------------------------
 function fact (n : int) : int      |  fact :: Int -> Int
   if n = 0 then                    |  fact n = if n == 0
     result 1                       |    then 0
   else                             |    else n * fact (n - 1)
     result n * fact (n - 1)        |  or:
   end if                           |  fact 0 = 1
 end fact                           |  fact n = n * fact (n - 1)


Comments

code:
Turing      | Haskell     
------------+-------------
 %          |  --     
 /* ... */  |  {- ... -} 


More to come.
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