8

I was wondering. Are there languages that use only pass-by-reference as their eval strategy?

Mechanical snail
  • 29,755
  • 14
  • 88
  • 113
Dervin Thunk
  • 19,515
  • 28
  • 127
  • 217

4 Answers4

6

I don't know what an "eval strategy" is, but Perl subroutine calls are pass-by-reference only.

sub change {
    $_[0] = 10;
}

$x = 5;
change($x);
print $x;  # prints "10"
change(0);  # raises "Modification of a read-only value attempted" error
Sean
  • 29,130
  • 4
  • 80
  • 105
  • Just putting a sutpid query here...is this idea of pass by value/reference is something dependent on the internal organization of a programming language or how it appears it to the programmer. I am asking this because most people say java emulates call-by-reference http://stackoverflow.com/questions/40480/is-java-pass-by-reference-or-pass-by-value and http://www.javaworld.com/article/2077424/learn-java/does-java-pass-by-reference-or-pass-by-value.html . But it appears as call by reference from programming point of view. Same way can we be sure that perl not using call by val in back?? – SamGhatak Jan 08 '17 at 18:30
1

How about Brainfuck?

Eric Mickelsen
  • 10,309
  • 2
  • 30
  • 41
1

VB (pre .net), VBA & VBS default to ByRef although it can be overriden when calling/defining the sub or function.

Alex K.
  • 171,639
  • 30
  • 264
  • 288
1

FORTRAN does; well, preceding such concepts as pass-by-reference, one should probably say that it uses pass-by-address; a FORTRAN function like:

INTEGER FUNCTION MULTIPLY_TWO_INTS(A, B)
INTEGER A, B
MULTIPLY_BY_TWO_INTS = A * B
RETURN

will have a C-style prototype of:

extern int MULTIPLY_TWO_INTS(int *A, int *B);

and you could call it via something like:

int result, a = 1, b = 100;

result = MULTIPLY_TWO_INTS(&a, &b);

Another example are languages that do not know function arguments as such but use stacks. An example would be Forth and its derivatives, where a function can change the variable space (stack) in whichever way it wants, modifying existing elements as well as adding/removing elements. "prototype comments" in Forth usually look something like

(argument list -- return value list)

and that means the function takes/processes a certain, not necessarily constant, number of arguments and returns, again, not necessarily a constant, number of elements. I.e. you can have a function that takes a number N as argument and returns N elements - preallocating an array, if you so like.

FrankH.
  • 17,675
  • 3
  • 44
  • 63
  • This does not demonstrate pass-by-reference. In the example you provide, `MULTIPLY_TWO_INTS` would have to modify `A` or `B`, and then we would have to see that the caller's version of `A` or `B` has changed after the call. – jpmc26 Jun 03 '16 at 22:48