Bonus task: ‘Challenge: TTY Formatting’

In Effekt, create a tiny & correct TTY (terminal) formatting library using effects and handlers.

Problem statement:

If you do red("Hello, " ++ bold("world") ++ "!!!") with naive definitions like red(s) := Escape::RED ++ s ++ Escape::RESET and bold(s) := Escape::BOLD ++ s ++ Escape::RESET, this produces <RED>Hello, <BOLD>world<RESET>!!!<RESET> which means that the exclamation marks are not red, which might be unexpected.

You must use effects and handlers to model this, restoring the state of the world correctly: the output of the call above should be <RED>Hello, <BOLD>world<RESET><RED>!!!<RESET> instead (note that the red is “reinstalled” after the reset).

The solution doesn’t need to be minimal (it’s fine to output “unnecessary” modifiers), the calls to red and bold can look different.

The solution should scale enough to be still nice when supporting “the whole spec”: different colours (exclusive), styles like bold, italic, underline, etc. (not exclusive).

There should be one handler that does all formatting and a different handler that doesn’t (for, let’s say, CI!).

Here are the relevant escapes for testing (feel free to comment out):

val RED = "\u001b[31m"
val BOLD = "\u001b[1m"
val RESET = "\u001b[0m"

You can also find them in tty in stdlib. (Just write import tty and jump to definition. They are called ANSI::RED etc…)

Hints:

we highly encourage you to experiment here, try printing things to see how they look in your terminal!
it’s perfectly OK to output <RED>, <BOLD> and <RESET> for testing purposes when working on the problem
bidirectional / higher-order effects might be helpful here

You can use the following editor to work on your solution:

def main() = ()

and REPL to run things:

main()

If you want to share your solution, you can use our playground which allows shareable links.

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