Re: [sc-users] recursion

[rohrhuber@xxxxxxxxxxxxxx]

and it it’s OK to have the array backwards, you can do it with a pure function:

(
~collatz_R = { arg num, col, limit = 1000;
	if((num != 1) and: { limit > 0 }) {
		~collatz_R.(
			if(num.even) { num.div(2) } { num * 3 + 1 },
			col,
			limit - 1
		)
	}.add(num)
};
)




> On 29. Dec 2019, at 01:37, <jamshark70@xxxxxxxxx> <jamshark70@xxxxxxxxx> wrote:
> 
> 
> Just a small point of coding style.
> 
> On Sun, Dec 29, 2019 at 6:16 AM <daniel-mayer@xxxxxxxx> wrote:
>> ((num == 1) or: { count >= limit }).if
> 
> If you look at other programming languages, constructions like
> "if(condition) true-block false-block" (with numerous syntax
> variations -- different ways of denoting the true and false branches)
> are common.
> 
> So a new user might look at this and think, why does SC write it bass-ackwards?
> 
> Answer: You don't have to. SC supports the syntax `if((num == 1) or: {
> count >= limit }) { true stuff... } { false stuff... }`.
> 
> Technically, `if` can be implemented as a method call, no different
> from 1.0.rand -- so it's completely valid to write
> `(condition-expression).if`. I used to do it this way, and there are
> still instances of that in my older public code.
> 
> My personal opinion is that this is not ideally readable. (One
> concrete reason is that the crucial keyword `if` ends up being buried
> in the middle of a line.)
> 
> ~collatz_R = { arg num, col, limit = 1000, count = 0;
>    if((num == 1) or: { count >= limit }) {
>        col = col.add(num);
>    } {
>        col = col.add(num);
>        ~collatz_R.(
>            if(num.even) { num.div(2) } { num * 3 + 1 },
>            col,
>            limit,
>            count + 1
>        )
>    }
> };
> 
> Oh, let's play with the code a bit. `col = col.add(num);` appears in
> both branches -- it will be done in both the true or false cases --
> so, move it outside the if. Then the "true" branch is empty, so,
> invert the condition:
> 
> (
> ~collatz_R = { arg num, col, limit = 1000, count = 0;
>    col = col.add(num);
>    if((num != 1) and: { count < limit }) {
>        // maybe a minor bug here:
>        // need to capture the recursion result
>        col = ~collatz_R.(
>            if(num.even) { num.div(2) } { num * 3 + 1 },
>            col,
>            limit,
>            count + 1
>        )
>    };
>    col
> };
> )
> 
> For fun/simplicity, you can drop the "count" argument as well by
> having "limit" count down:
> 
> (
> ~collatz_R = { arg num, col, limit = 1000;
>    col = col.add(num);
>    if((num != 1) and: { limit > 0 }) {
>        col = ~collatz_R.(
>            if(num.even) { num.div(2) } { num * 3 + 1 },
>            col,
>            limit - 1
>        )
>    };
>    col
> };
> )
> 
> hjh
> 
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