2. Re: function/procedure arguments

• Posted by ghaberek (admin) Mar 13, 2018
• 1156 views

function tttest(object t) 
  t={} 
  return 1 
end procedure 
 
sequence s11 = {1,2,3} 
integer xx = tttest(s11) 

This is a good question. Not everyone is aware of how Euphoria works internally. The manual states the following here: 4.2.1.1 procedures (emphasis mine)

Euphoria uses object reference counting with copy-on-write. So if you pass an object to a routine and do not modify the object, it's effectively been passed by reference. If you modify the value then a new object is created in place with the new value.

If you'd like to manage references to objects, then I suggest using the Pseudo Memory library. This allows you to "allocate" an object and then pass around a reference to it while its value lives in the global ram_space sequence.

include std/eumem.e 
 
function tttest(integer t) 
  ram_space[t] = {} 
  return 1 
end function 
 
integer s11 = eumem:malloc() 
ram_space[s11] = {1,2,3} 
integer xx = tttest(s11) 

-Greg

4. Re: function/procedure arguments

• Posted by _tom (admin) Mar 13, 2018
• 1127 views

Here is something that is missing from the documentation. However, the answer you wanted comes from Greg.

_tom

Passing Values to a Routine

A parameter is "a variable you declare in the signature of a routine." An argument is "is the something you pass to a parameter when you call a routine."

( Note that authors are always getting parameter and argument confused. Some authors resort to calling an argument a formal parameter. )

You can imagine three ways of passing the something to a parameter:

• pass by value
• pass by reference
• pass by elision

The question is, what does Euphoria do?

Pass by value (Euphoria just looks like this)

The parameter is a full copy of the argument. That means more memory and time for the copy operation. Changes to the parameter do not change the original argument value.

Pass by reference (Never in Euphoria)

The parameter becomes a reference back to the argument. Copying just a reference needs no extra memory and is very fast. Changes to the parameter also changes the original argument value.

Pass by elision (Euphoria does this)

The parameter receives a reference to the argument. Copying just a reference needs no extra memory and is very fast. The trick in Euphoria languages is that changes to the original arguments are not allowed. Changes to a parameter are localized to the routine--they do not alter the original. In Euphoria the elision of an argument means copy just what you need and reference everything else.

The word elision means "omission by intent or design." Thus elision is the omission of a sound when speaking. Instead of I am you say I'm. Instead of let us you say let's.

In Euphoria elision means:

sequence s = repeat( 0, 100_000_000 )  --(1) a huge sequence 
                                       --    with many many items 
 
function foo( object x )  --(2) `looks-like` a huge copy job is needed 
                          --    actually `x` will be a reference to `s` 
 
    x[1] += 1             --(3) a parameter change now requires 
                          --    some local memory, not much though 
 
    return x[1]           --(4) original argument is not changed 
                          --(5) cost (time and memory) for a local change is negligible 
end function 
 
? foo( s ) 
--> 1                     --(6) pass-by-elision explains why Euphoria is 
                          --   * safe 
                          --   * fast 

6. Re: function/procedure arguments

• Posted by _tom (admin) Mar 13, 2018
• 1119 views

Work in progress...

I did a quick edit on the previous entry.

The word "elision" shows up in compiler optimizations that seem to work like Euphoria.

Yes, elision is not a great word.

• Euphoria is not pass-by-value (but it looks like it)
• Euphoria is not pass-by-reference (but does uses references)
• Euphoria is pass by [ insert best word ... ]

Everyone, give me a new word.

Emulating pass-by-reference is a different topic

_tom

8. Re: function/procedure arguments

• Posted by petelomax Mar 13, 2018
• 1061 views

I just use "defaulted parameters".

10. Re: function/procedure arguments

• Posted by _tom (admin) Mar 13, 2018
• 1075 views

I have seen all kinds of variations of how parameter is used. These authors have not looked at wikipedia.

In the days before computers it was clear that an argument to a function was the supplied value:

sin(x)

`x` is the argument to a trigonometric function

That leaves parameter as the variable defined in a function signature.

As a supporter of Luddites I use this as my starting point.

_tom