DIP 1027---String Interpolation---Community Review Round 1

[Petar]

On Thursday, 12 December 2019 at 17:03:53 UTC, Atila Neves wrote:
> On Thursday, 12 December 2019 at 17:01:01 UTC, Adam D. Ruppe 
> wrote:
>> On Thursday, 12 December 2019 at 15:41:54 UTC, aliak wrote:
>>> [...]
>>
>> The javascript version is allowed to return whatever it wants. 
>> The default one returns string but you can do other things 
>> with it too like return objects or functions or whatever.
>>
>> [...]
>
> It'd be great if you could expand on this with a list of 
> examples of what D could do.

Tagged template literals are indeed quite nice in JS. Here's an 
example from the chalk npm package [1]:

```js
// Plain template literals (a.k.a. built-in string interpolation):
const str1 = `
CPU: ${chalk.red("90%")}
RAM: ${chalk.green("40%")}
DISK: ${chalk.yellow("70%")}
`;

// Same example but with tagged template literals - more DRY:
const str2 = chalk`
CPU: {red 90%}
RAM: {green 40%}
DISK: {yellow 70%}
`;

// Tagged template literals + interpolation of variables:
const cpu = 90;
const ram = 40;
const disk = 70;

const str3 = chalk`
CPU: {red ${cpu}%}
RAM: {green ${ram}%}
DISK: {yellow ${disk}%}
`;

Here's another example, this case from the es2015-i18n-tag 
library [2] that applies translations, locale and currency 
formatting:

const name = 'Steffen'
const amount = 1250.33
console.log(i18n`Hello ${ name }, you have ${ amount }:c in your 
bank account.`)
// Hallo Steffen, Sie haben US$ 1,250.33 auf Ihrem Bankkonto.
```

The D analog of a function that can be used as tagged template 
string literal would be:

```d
string interpolate(Args...)(string[] parts, Args args)
{
     import std.algorithm.iteration : joiner;
     import std.conv : text;
     import std.range : roundRobin;

     string[Args.length] stringifiedArgs;

     static foreach (idx, arg; args)
         stringifiedArgs[idx] = text(arg);

     return parts.roundRobin(stringifiedArgs[]).joiner.text;
}

static import term; // Assume some ANSI term coloring library

const string res = i"
CPU: ${term.red("90%")}
RAM: ${term.green("40%")}
DISK: ${term.yellow("70%")}
".interpolate;
```

[1]: https://github.com/chalk/chalk
[2]: https://github.com/skolmer/es2015-i18n-tag