OpenEuphoria

Re: variable declaration reset

• Posted by _tom (admin) Apr 17, 2022
• 1372 views

Phix is working as expected.

JavaScript is working in a plausible, internally consistent, ?

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Consider the creation of a variable, which is a two step process.

• instantiate a type and give it a name integer prev

• • prior to this, any code that used the name ''prev'' crashes Phix
  • just after this moment: ? object(prev) is False.

• assign a value prev := s[i]

• • after this moment: ? object(prev) is True.
  • since it is a loop, prev is now in-scope before the declaration, next time the loop is performed ... this makes sense, but maybe not obviously

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• observations
  • prev is out-scope after ''end for''

• • it makes no sense (in a compiled program) for ''integer prev'' to be duplicated ''i'' number of times that is a waste of energy
  • the variable is created exactly once in the loop

• • in a traditional interpreter (one-line-at-time design) it is not surprising that ''integer prev'' is actually duplicated for every loop iteration which causes a "reset"... very inefficient

• • I would expect ''integer prev'' to be ignored in a loop after the first encounter

• • once the loop goes past ''one iteration'', then prev is in-scope from the top of the loop ? object(prev) just before the declaration returns True

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sidebar

This seems to be more idiomatic for OE/Phix:

for i=2 to length(s) do 
	if s[i-1] == s[i] then 
		? { s[i-1], s[i] } 
	end if 
 
	---- optional 
	integer curr,prev 
	{curr,prev} := { s[i-1], s[i] } 
end for 

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question

It would be interesting if a statement existed that would "undo" an assignment and "reset" a variable to an assigned state so ? object(prev) does return False

be well
_tom

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