# Function and procedure behave differently with the same code in Mozart Oz?

### Tags:

#### mozart

I try printing out the Fibonacci sequence in Oz using 2 approach : function and procedure using Emac as editor. Procedure goes here :

``````declare
fun {Fibo N}
case N of
1 then 1
[] 2 then 1
[] M then {Fibo (M-1)} + {Fibo (M-2)}
end
end
declare
proc {Loop K}
if K ==1 then  {Browse K}
else
{Loop K-1}
{Browse {Fibo K}}
end
end
{Loop 10}
``````

and function:

``````declare
fun {Fibo N}
case N of
1 then 1
[] 2 then 1
[] M then {Fibo (M-1)} + {Fibo (M-2)}
end
end
declare
fun {Loo L}
if L ==1 then  {Browse L}
else
{Loo L-1}
{Browse {Fibo L}}
end
end
{Loo 10}
``````

The problem is the only Procedure "Loop" works. Result is:

``````1
1
2
3
5
8
13
21
34
55
``````

Function "Loo" doesn't and it throws some hard-to-understand errors:

``````%********************** static analysis error *******************
%**
%** illegal arity in application
%**
%** Arity found:          1
%** Expected:             2
%** Application (names):  {Loo _}
%** Application (values): {<P/2> _<optimized>}
%** in file "Oz", line 13, column 6

%********************** static analysis error *******************
%**
%** illegal arity in application
%**
%** Arity found:          1
%** Expected:             2
%** Application (names):  {Loo _}
%** Application (values): {<P/2> 10}
%** in file "Oz", line 17, column 0
%** ------------------ rejected (2 errors)
``````

I still don't know why. As I think function and procedure has similar effect in OZ.

257

#### Duc Tran

What is the function of Oz?

Oz provides the salient features of object-oriented programming including state, abstract data types, objects, classes, and inheritance. It provides the salient features of functional programming including compositional syntax, first-class procedures/functions, and lexical scoping.

How do I run an Oz program?

On olympus Mozart/Oz system is found in /local/gnu/bin/ , which should be in your PATH by default. (Thus you shouldn't have to do anything special to set this up.) To start the Mozart/Oz system, simply issue the command oz at the shell's prompt.

Functions must be called either with function call syntax:

``````_ = {Loo 10}
``````

``````{Loo 10 _}
``````

`_` is pronounced "don't care" and means that the value of the variable is not needed.

Also, functions must return a value by having an expression as the last part of every branch. So your fixed `Loo` function would look like this:

``````fun {Loo L}
if L == 1 then
{Browse L}
unit
else
_ = {Loo L-1}
{Browse {Fibo L}}
unit
end
end
_ = {Loo 10}
``````

However, using a function for looping like this does not make much sense if you don't have anything interesting to return. Maybe what you really want is to build a list and return it as the result?

153