Re: Proposal: Add IsString instance for (Maybe a) to base

On Fri, Jul 12, 2013 at 2:45 AM, John Lato wrote:

On Fri, Jul 12, 2013 at 2:13 PM, Roman Cheplyaka wrote:

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* John Lato [2013-07-12 13:56:31+0800]

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The programmer is being explicit; the type specifies the value is a Maybe. If it weren't, the Just wouldn't be inserted.

Not necessarily — take Simon's original example:

(shell "ls -l") { cwd = "/home/me" }

If I didn't know the type of 'cwd', it would never occur to me while reading this code that you can supply Nothing there.

So? If you're just reading the code, it doesn't matter. If you want to

It does to me! Concrete types help me read. I have a lot of trouble understanding libraries that make extensive use of typeclasses, both reading their documentation and reading code that uses them.

OverloadedStrings (and number literals) are already a mess for this. Currently, we have

(shell "ls -l") { cwd = Just "/home/me" }

If I want to replace that literal with a value and I don't know the type of 'cwd', I already need to look it up. Otherwise I might try to do something like this:

dirFromUser <- Text.getLine (shell "ls -l") { cwd = Just dirFromUser }

I probably wouldn't, because I know the process package uses Strings. In general though I agree, with overloading there's a bit of a mess, but that's not license to expand the mess.

A decent IDE helps a lot if you don't know the types of things in your code. Everyone should use one.

It sounds reasonable in theory, but I've never seen an IDE I would call "decent".