Com S 541 Lecture -*- Outline -*-

* Introduction to Haskell

** interaction (Thompson chapter 2, replaces Davie 2.1)
        see also the on-line documentation for Hugs
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     INTERACTING WITH THE INTERPRETER

$ hugs 
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||   || Version: Nov 2003

Haskell 98 mode: ...

Type :? for help
Prelude> 

------------------------------------------
	... hugs
	... :quit

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	MORE INTERACTION
Prelude>  

Prelude>  :type 1
1 :: Num a => a
Prelude>  3 + 4
7 :: Int
Prelude>  (+) 3 4
7 :: Int
Prelude>  216 * 34
7344 :: Int
Prelude>  7344 / 34
216.0 :: Double
Prelude>  7 / 3
2.33333 :: Double
Prelude>  div 7 3
2 :: Int
Prelude>  7 `div` 3
2 :: Int
Prelude>  7 `rem` 3
1 :: Int
Prelude>  7 `divRem` 3

ERROR: Undefined variable "divRem"
Prelude>  7 `quotRem` 3
(2,1) :: (Int,Int)
Prelude>  :type 7 `quotRem` 3
quotRem 7 3 :: Integral a => (a,a)
------------------------------------------
	... ? 1
	    1 :: Int

	(Unlike Davie, you just end expressions with a newline,
		they can only be on one line.)

	Another correction, p. 13, use quotRem instead of divRem

	See handout and the manual page for more details

------------------------------------------
	WORKING WITH FILES

Prelude>  :load "Fact.hs"
Fact> fact
fact {dict} {dict} :: Int -> Int
Fact> :type fact
fact :: (Num a, Enum a) => a -> a
Fact> fact 4
24 
Fact> fact 100
0
Fact> :edit Fact.hs
Fact> :reload
                   
Fact> :type fact
fact :: Integer -> Integer
Fact> fact 100
9332621544394415268169923885626670049...
Fact> 
Fact> :q
[Leaving Hugs]
------------------------------------------

        for the first version of Fact.hs, use

> fact n = product [1 .. n]

        it works to say fact (toInteger 100),
                when used in the interpreter,
                showing the result makes the literal acquire type Int

	the :reload command reloads the file you're working on,
		if you don't want to invoke the editor from inside Hugs.

	use
		setenv EDITOR vi
	to change the default editor to vi

------------------------------------------

popeye 15% hugs Fact.hs
   [...]

Reading file "... Prelude.hs"
Reading file "Fact.hs":
                   
Type :? for help
Fact> fact 8
40320
Fact> :q
[Leaving Hugs]
------------------------------------------

------------------------------------------
		LITERATE SCRIPTS

file foo.lhs:
     ==============================
                A TITLE

     Some text, whatever you want..

     > -- part of a Haskell prog
     > hd (x:_) = x
     
     The blank lines surrounding
     the program are mandatory.

     This file should have a .lhs
     suffix, or use the +l argument
     to the interpreter.
     ==============================


Prelude> :load "foo.lhs"
Main> hd (3 : (4 : []))
3 :: Int
------------------------------------------

	program parts have > as first character on line,
		so even this file can be processed as a program!
		use hugs +l introduction.txt