Convert haskell Int with leading zero to String

Question

Suppose I have a variable of type Int = 08, how can I convert this to String keeping the leading zero?

For instance:

v :: Int
v = 08

show v

Output: 8

I want the output to be "08".

Is this possible?

Answer 1

Use Text.Printf.printf:

printf "%02d" v

Make sure to import Text.Printf.printf first.

Answer 2

Its 8, not 08 in variable v. Yes, you assigned it 08 but it receives 8. Thats the reason show method displayed it as 8. You can use the work around given by Mipadi.

Edit:

Output of a test.

Prelude> Text.Printf.printf "%01d\n" 08
8
Prelude> Text.Printf.printf "%02d\n" 08
08
Prelude> Text.Printf.printf "%03d\n" 08
008

Output of another test.

Prelude> show 08
"8"
Prelude> show 008
"8"
Prelude> show 0008
"8"

I hope you get the point.

Edit:

Found another workaround. Try this,

"0" ++ show v

Answer 3

Depending on what you are planning to do you might want to store the "08" as a string and only convert to int when you need the value.

Answer 4

The printf way is probably best, but it's easy enough to write your own function:

show2d :: Int -> String 
show2d n | length (show n) == 1 = "0" ++ (show n)
         | otherwise = show n

Works as follows:

Prelude> show2d 1
"01"
Prelude> show2d 10
"10"
Prelude> show2d 100
"100"