Re: A little bit of golf

[Hisham <h@...>]

On 8 April 2015 at 04:04, Dirk Laurie <dirk.laurie@gmail.com> wrote:
> 2015-04-08 2:12 GMT+02:00 Hisham <h@hisham.hm>:
>> Hi all,
>>
>> So here's a little problem that some of you might enjoy playing with
>> in case you're bored.
>>
>> Let's play "variable expansion". We want to convert "Hello, $planet!"
>> to "Hello, Earth!" given { planet = "Earth" }, but we also want it to
>> support "Hello, ${planet}!".
>>
>> That is, we want to perform "variable expansion" in a string s, so
>> that given a table of "variables" we want to expand every $foo or
>> ${foo} in s to the value of variables.foo.
>>
>> HOWEVER, we don't want recursive expansion (ie, if the value of
>> variables.foo is "$bar", then we _don't_ want it expanded to the value
>> of variables.bar).
>
> I.e. you wish to remove the restriction on the third line
> of the docstring of ml.expand (from Microlight).
>
> --- expand a string containing any `${var}` or `$var`.
> -- If the former form is found, the latter is not looked for, so
> -- pick _either one_ of these forms consistently!
> -- Substitution values should be only numbers or strings.
> -- @param s the string
> -- @param subst either a table or a function (as in `string.gsub`)
> -- @return expanded string
>
>> Can you suggest any nicer and/or shorter solution?
>>
>> Ah! NO LPEG ALLOWED! :)
>
> math.randomseed(os.clock())
> function password()  return (("."):rep(32):gsub(".",
>   function() return string.char(math.random(256)-1) end))
> end
>
> Now make two tables: one containing the original keys
> and a password for each, the other containing those
> passwords as keys with the original values.
>
> Three times gsub:
>   the ${var} forms with the first table,
>   the $var forms with the first table,
>   the passwords with the second table.
>
> If you are scared this might not work, better not use
> ATMs any more either.

Haha, nice. :) The passwords would have to have some sort of constant
marker for us to be able to perform the third gsub, right?

-- Hisham