Given the code below:

```
import Data.List;
main = (readLn :: IO [Integer]) >>= print . subsequences
```

It takes a list of integers from standard input (for example `[1,2,3]`

) and outputs something like:

`[[],[1],[2],[1,2],[3],[1,3],[2,3],[1,2,3]]`

I want it to be like this:

`{},{1},{2},{1,2},{3},{1,3},{2,3},{1,2,3}}`

so my goal is to replace every `[`

and `]`

in the result string with `{`

and `}`

respectively.

How can I achieve this?

Answer:

All you need is love and to split `print`

into `putStrLn . show`

and then add a simple `map`

in-between which does the conversion:

```
main :: IO ()
main =
let fn '[' = '{'
fn ']' = '}'
fn c = c
in (readLn :: IO [Integer]) >>= putStrLn . map fn . show . subsequences
```

The above code, given `[1, 2, 3]`

, will output:

`{},{1},{2},{1,2},{3},{1,3},{2,3},{1,2,3}}`

If this is a code golf, then you could have (**106 characters**):

```
f '[' = '{';f ']' = '}';f c = c;main = (readLn :: IO [Integer]) >>= putStrLn . map f . show . subsequences
```

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