trace

The trace can be used in conjunction with the option command in Darwin(see §) or it can be used as a Darwin command directly by passing a name of a procedure as a parameter. When applied to procedures, the trace command directs Darwin to display the result of every executed statement accompanied with the value of the parameters at the entry point to the routine and the value being returned. The option trace combination must follow any local and global variable declarations after the routine declaration.

> Sum := proc(val : real)
>   local total;
>   option trace;  
>                    # must follow local and global variable declarations
>
>   total:=0;
>   for i from 1 to val do
>     total :=total+i;
>   od;
>   total;
> end;
> Sum(5);
{--> enter Sum, args = 5
total := 0
total := 1
total := 3
total := 6
total := 10
total := 15
15
<-- exit Sum = 15}
15

Alternatively, we could omit the option trace command and invoke trace as follows.

> Sum := proc( val : real )
>   local total;
>
>   total:=0;
>   for i from 1 to val do
>     total :=total+i;
>   od;
>   total;
> end;
> trace(Sum);
> Sum(5)