OpenEuphoria

problems with the scoping in eu4

• Posted by bill Jan 07, 2011
• 2192 views

1 Shadowing:

One cannot redefine variable names eg

integer f = 0 
... 
sequence f = {} 

is an error

likewise :

for i = 1 to 10 do 
  puts(1,sprintf("%d, ",2*i) 
end for 
... 
for i = 1 to 20 do .. <= error 

however this is different:

integer f = 2 
function ff(sequence f = "ok") 
  return f 
end function 
puts(1,sprintf("%s\n",ff())) => ok 
puts(1,sprintf("%d, ",f)     => 2 

2 while do problems:
Cannot initialise a counter inside a loop

integer r = 4 
while r > 0 do 
  integer i = 0 
  puts(1,sprintf("%d, ",i) 
  i += 1 
  r -= 1 
end while 

prints: 0, 0, 0, 0

while r > 0 with entry do 
  integer i = 0 
  puts(1,sprintf("%d, ",i) 
  r -= 1 
entry 
  i += 1  <= at runtime i has no value 
end while 

3 while with entry seems quite unnecessay given exit (using ada loop, end loop & exit when).

    sequence ret = {} 
    loop  
	   from = find_from (x, source, from) 
	   exit when from = 0 
       ret &= from  
       from += 1  
    end loop  

Exit can take a label.

Now the code executes in order, there is no jump into scope.

4 another reason not to use while with entry (readability).
It places the entry code below any inner loop

5 Switch has problems as well.

switch a 
case x then 
  integer i = 0 
  puts(1, sprintf("%d",i)) 
  i += 1 
case x+1 then 
  puts(1, sprintf("%d",i)) 
  i += 1## 
... 

This should compile but cannot work with a = (x+1)
Any declaration before case else allow a jump into scope.

6. Commentary:
ada has anonymous blocks syntax
eg an in-line swap of integers x, y

declare 
  t integer := x 
begin 
  x := y 
  y := t 
end 

A possible while syntax could be

while condition 
declare  
  type id [= value] 
do 
  .. 
end 

I am not saying this is how things should be done but these aspects of Euphoria make the new features difficult to impossible to use.

[matt: added eucode tags]