Haskell_Notes_2

2. Starting Out
==========

After the installation in Windows:

C:\Program Files\Haskell Platform\2011.2.0.1\winghci\winghci.exe


double click and run.


GHCi, version 7.0.3: http://www.haskell.org/ghc/  :? for help
Loading package ghc-prim ... linking ... done.
Loading package integer-gmp ... linking ... done.
Loading package base ... linking ... done.
Loading package ffi-1.0 ... linking ... done.
Prelude> 


Few Points:

1. GHCi -> Glasgow Haskell Compiler interactive mode
2. Latest version as of 30th July 2011 - 7.0.3
3. Couple of packages are loaded - ghc-prim, integer-gmp, base, ffi-1.0
4. The default prompt we get is: Prelude
-------------------------------

Prelude> :set prompt ghci
ghci :set prompt "ghci> "
"ghci> " :set prompt ghci> 
ghci>  
---------------------------------

ghci>  180

180

ghci>  1*0

0

ghci>  1/0

Infinity

ghci>  10/3

3.3333333333333335

ghci>  10/4

2.5

ghci>  1==0

False

ghci>  10000000.0000000000001==10000000.0000000000001

True

ghci>  10000000.0000000000001==10000000.0000000000000 
True

ghci>  10000000.0000000000001==10000000.0000000000000000

True

ghci>  10000000.0000000000001==10000000.0000000000000001

True

ghci>  10000000.0000000000001==10000000.0000000100000001

False

ghci>  10000000.0000000000001==10000000.0000000000001

True

ghci>  10000000.0000000000001==10000000.0000000000009
True



ghci>  10+100/20
15.0
ghci>  (10+100)/20
5.5
ghci>  5 * -3


<interactive>:1:1:
    Precedence parsing error
        cannot mix `*' [infixl 7] and prefix `-' [infixl 6] in the same infix expression


ghci>  5 * (-3)
-15
ghci>

Boolean algebra

ghci>  true


<interactive>:1:1: Not in scope: `true'


ghci>  True
True

ghci>  True & True

<interactive>:1:6: Not in scope: `&'

ghci>  True && True

True

ghci>  True &&& True

<interactive>:1:6: Not in scope: `&&&'

ghci>  True && && True

<interactive>:1:9: parse error on input `&&'

ghci>  True &&           True

True

ghci>  True &&       False    True

<interactive>:1:15:

    The function `False' is applied to one argument,

    but its type `Bool' has none

    In the second argument of `(&&)', namely `False True'

    In the expression: True && False True

    In an equation for `it': it = True && False True

True 

False

&&

||

not

Case Sensitive

Comment? 

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

Character Type:    'a' 

string type: "hello"

Equal to and Not Equal to:

ghci> 1==1

True

ghci> 1/=1

False

ghci> 1/=2

True

Exceptions:

ghci>  5 == True

<interactive>:1:1:

    No instance for (Num Bool)

      arising from the literal `5'

    Possible fix: add an instance declaration for (Num Bool)

    In the first argument of `(==)', namely `5'

    In the expression: 5 == True

    In an equation for `it': it = 5 == True

ghci>  'a' + 'b'

<interactive>:1:5:

    No instance for (Num Char)

      arising from a use of `+'

    Possible fix: add an instance declaration for (Num Char)

    In the expression: 'a' + 'b'

    In an equation for `it': it = 'a' + 'b'

ghci>  "he" + "he"

<interactive>:1:6:

    No instance for (Num [Char])

      arising from a use of `+'

    Possible fix: add an instance declaration for (Num [Char])

    In the expression: "he" + "he"

    In an equation for `it': it = "he" + "he"