Re: Can zsh `else` reserved keyword command be aliased and the lexem itself be repurposed as `fi` keyword command?

[mathieu stumpf guntz <psychoslave@xxxxxxxxxxxxxxxxx>]

Hello Bart,

First, thank you for having taken some time to write this detailed answer.


Le 29/12/2017 à 09:38, Bart Schaefer a écrit :
> If you haven't already, go read https://askubuntu.com/a/590335 which
> was linked from
> https://stackoverflow.com/questions/47999451/can-zsh-buildtins-be-aliased
>
> Your hypothetical "keyword" would have to itself be a keyword (and
> thus not a command).
Yes, I had red it, and I even took time to read it again in case I 
missed something, but I didn't find what. Actually, it says "aliases can 
be used to alias keywords!", so it made me more confident about the fact 
that it might be possible.

I understand that the hypothetical "keyword" callable-stuff should be of 
type keyword however (however it's tricky to make clear sentences about 
such an intricated topic). I don't have in mind the whole interpretation 
pipeline in mind, an [acitivity 
diagram](http://plantuml.com/activity-diagram-beta) would be welcome 
here. However, it does  make  sense that the tool to make a substitution 
at some level must be at least at the same type level or in a type which 
is interpreted earlier.

> What's the underlying reason for doing this?
Admitedly, it's an interesting challenge which enable to grab a little 
more knowledge on the shell.
>   That is, aside from the
> overall desire to write in Esperanto (?),  I get wanting "alie" to
> mean the same thing "else" means, but not why "else" should mean "fi".
Because "else" could litteraly be translated "out of if". Maybe [12.3.2 
Directional prepositions / Grammar - 
lernu.net](https://lernu.net/en/gramatiko/direktaj_prepozicioj) can give 
a good grab on this. And Esperanto is an agglutinate language, you can 
concatenate any set of lexemes and it will make sense (most of the 
time). And "el-" as a suffix is common place. But it's difficult to find 
resource in English to appreciate this, the online [plena ilustrita 
vortaro](http://vortaro.net/#el) does give an account of this practice – 
but in Esperanto.

> Even in your "alie echo 'mirinda mondo'"  example it looks like "else"
> is meant to act as "fi;else" so that you can continue with more of the
> sentence.
I'm not sure to understand what you mean here.

But for the sake of the example, you might consider a more complete 
"translation":

   alias se='enable -r else; if'
   alias alie='else'
   disable -r else
   alias else=":fi ; disable -r else"
   alias tiam='then'
   alias ja='['
   alias -g ope=']'
   alias -g plie='-a'
   alias -g vakua='-z'

   alias vera='true'
   alias eĥu='echo'

   se ja vakua $signvico plie vera ope nu tiam # [1]
        eĥu "la signvico estas vakua!"
   alie
        eĥu "la signvico ne estas vakua!"
   else

[1] you might translate that as "if indeed $signvico (is) empty and 
furthermore (it's) true, all that together, well, then…".

In that peace of code, "alie" really is "else", or "otherwise" if you 
prefer.

> This is doomed to failure, because complex shell syntax is fully
> parsed before it is executed.  Your "disable" or "enable" has to take
> place before the parsing step, because it won't be executed during the
> parse.  Some extremely simple cases might appear to work at the
> command prompt, but as soon as you embed them in a larger structure
> like a function body they will fail.
Thus my demand in my other reply, is there a command that say to the 
shell, "ok, stop to eat the stream here and process the chunck of code 
you already buffered so far". As far as I understand, that's what a line 
break usually do. I tried to add one in the alias, including by using a 
heredoc string, but this doesn't work.
> What is needed is an alias that ends recursive replacement.  Normally
> one does this by including quoting (e.g., a leading backslash) in the
> value of the alias, but that doesn't help in this case because it
> prevents the replacement from being considered a keyword as well.
> There may be a clever way to accomplish this -- recursion stops if
> replacement results in a previously replaced alias, for example, to
> avoid infinite loop -- but I haven't worked out an answer.
Well, I stay tune if anyone find any way to solve this challenging goal. ;)

Cheers