IHaskell Notebook Test 1

In [1]:

    

-- First of all, we can evaluate simple expressions.
3 + 5
"Hello, " ++ "World!"


    

    






8






    






"Hello, World!"

In [2]:

    

it1


    

    






"Hello, World!"

In [3]:

    

-- Unlike in GHCi, we can have multi-line expressions.
concat [
  "Hello",
  ", ",
  "World!"
  ] :: String


    

    






"Hello, World!"

In [4]:

    

thing :: String -> Int -> Int
thing "no" _ = 100
thing str int = int + length str

thing "no" 10
thing "ah" 10


    

    






100






    






12

In [5]:

    

print "What's going on?"


    

    






"What's going on?"

In [6]:

    

-- We can disable extensions.
:ext NoEmptyDataDecls
data Thing


    

    




<interactive>:1:1: error:
    • ‘Thing’ has no constructors (EmptyDataDecls permits this)
    • In the data declaration for ‘Thing’

In [7]:

    

-- And enable extensions.
:ext EmptyDataDecls
data Thing


    

In [8]:

    

-- Various data declarations work fine.
data One
     = A String
     | B Int
     deriving Show

print [A "Hello", B 10]


    

    






[A "Hello",B 10]

In [9]:

    

-- We can look at types like in GHCi.
:ty 3 + 3


    

    





3 + 3 :: forall a. Num a => a

In [10]:

    

:opt no-pager


    

In [11]:

    

-- What is the Integral typeclass?
:info Integral


    

    










    





class (Real a, Enum a) => Integral a where
  quot :: a -> a -> a
  rem :: a -> a -> a
  div :: a -> a -> a
  mod :: a -> a -> a
  quotRem :: a -> a -> (a, a)
  divMod :: a -> a -> (a, a)
  toInteger :: a -> Integer
  {-# MINIMAL quotRem, toInteger #-}
  	-- Defined in ‘GHC.Real’
instance Integral Word -- Defined in ‘GHC.Real’
instance Integral Integer -- Defined in ‘GHC.Real’
instance Integral Int -- Defined in ‘GHC.Real’

In [12]:

    

import IHaskell.Display

data Color = Red | Green | Blue

instance IHaskellDisplay Color where
  display color = return $ Display [html code]
    where
      code = concat ["<div style='font-weight: bold; color:"
                    , css color
                    , "'>Look!</div>"]
      css Red   = "red"
      css Blue  = "blue"
      css Green = "green"

Red
Green
Blue


    

    





Look!






    





Look!






    





Look!

In [13]:

    

-- There is also hlint integration enabled by default.
-- If you write sketchy code, it will tell you:
f :: Int -> Int
f x = x + 1

-- Most warnings are orange...
f $ 3

do
  return 3


    

    





Redundant $
Found:
f \$ 3
Why Not:
f 3
Redundant do
Found:
do return 3
Why Not:
return 3






    






4






    






3

In [14]:

    

:help


    

    






The following commands are available:
    :extension <Extension>    -  Enable a GHC extension.
    :extension No<Extension>  -  Disable a GHC extension.
    :type <expression>        -  Print expression type.
    :info <name>              -  Print all info for a name.
    :hoogle <query>           -  Search for a query on Hoogle.
    :doc <ident>              -  Get documentation for an identifier via Hoogle.
    :set -XFlag -Wall         -  Set an option (like ghci).
    :option <opt>             -  Set an option.
    :option no-<opt>          -  Unset an option.
    :?, :help                 -  Show this help text.
    :sprint <value>           -  Print a value without forcing evaluation.

Any prefix of the commands will also suffice, e.g. use :ty for :type.

Options:
  lint        – enable or disable linting.
  svg         – use svg output (cannot be resized).
  show-types  – show types of all bound names
  show-errors – display Show instance missing errors normally.
  pager       – use the pager to display results of :info, :doc, :hoogle, etc.

In [15]:

    

x = ['a'..'z']
x !! 3
:sprint x


    

    






'd'






    





x = 'a' : 'b' : 'c' : 'd' : _

In [16]:

    

-- If your code isn't running fast enough, you can just put it into a module.
module A.B where

fib 0 = 1
fib 1 = 1
fib n = fib (n-1) + fib (n-2)


    

In [17]:

    

-- The module is automatically imported unqualified.
print $ A.B.fib 20
print $ fib 20


    

    






10946






    






10946

In [18]:

    

f 3


    

    




<interactive>:1:1: error: Variable not in scope: f :: Integer -> t

In [19]:

    

import qualified A.B as Fib

Fib.fib 20
fib 20


    

    






10946






    






10946