Haskell: Specifying type to a variable

In my previous post, I explained about how to define a variable. We can also specify type to a variable.

Syntax

variable :: Type

Sample.hs

name :: String
pin :: Integer

name = "Krishna"
pin = 123456

Prelude> :load Sample.hs
[1 of 1] Compiling Main             ( Sample.hs, interpreted )
Ok, modules loaded: Main.
*Main> 
*Main> name
"Krishna"
*Main> 
*Main> pin
123456
*Main> 
*Main> :t name
name :: String
*Main> 
*Main> :t pin
pin :: Integer

You can combine the binding and type declaration in one line like below.

Sample.hs

name = "Krishna" :: String
pin = 123456 :: Integer

If all variables has same type, then you can declare them in same line like below.

Sample.hs

a, b, c, d :: Integer
e, f :: String

a = 10
b = 11
c = 12
d = 13

e = "ptr"
f = "nayan"

*Main> :load Sample.hs
[1 of 1] Compiling Main             ( Sample.hs, interpreted )
Ok, modules loaded: Main.
*Main> 
*Main> (a, b, c, d, e, f)
(10,11,12,13,"ptr","nayan")

By enabling scoped type variables, you can specify the type signature and assign a values to different type variables in same line. ScopedTypeVariables is a GHCi extension.

Sample.hs

{-# LANGUAGE ScopedTypeVariables #-}

(empId :: Integer, name :: String, salary :: Double) = (10, "Sudhir", 5.7)

*Main> :load Sample.hs
[1 of 1] Compiling Main             ( Sample.hs, interpreted )
Ok, modules loaded: Main.
*Main> 
*Main> empId
10
*Main> 
*Main> name
"Sudhir"
*Main> 
*Main> salary
5.7

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