Question regarding performance hacks about metta-examples HOT 6 OPEN

Iterative variant should be quicker, but in current metta interpreter's state it is quite opposite due to interpreter cashes all calls during evaluation

To me the second variant is quicker. In both minimal MeTTa and Rust interpreter.

from metta-examples.

Apparently, nested ifs may add some overhead. However, the code in these examples should be pretty straightforwardly compilable, which we may have in the near future. At the same time, the code like this

(= (fac2 0) 1)
(= (fac2 $x)
    (if (> $x 0)
        (* (fac2 (- $x 1)) $x)
        (empty)))

uses non-determinism for a deterministic function, which is definitely not an idiomatic way to implement it, and involves (empty), which requires additional explanations. Even if it is faster, it's not a good idea for a tutorial to show such code.
There are other ways to implement fact of fib, and to avoid nested ifs for mutually exclusive branches (instead of using non-determinism which is for non-exclusive branches), e.g. with the use of case:

(= (fac3 $x)
   (case $x
    ((0 1)
     ($_ (* (fac3 (- $x 1)) $x)))))

Whether to use case or not may depend on how the tutorial is organized.
Maybe, transforming this code

(= (fib $n)
    (if (== $n 0)
        0
        (if (== $n 1)
            1
            (+ (fib (- $n 1)) (fib (- $n 2))))))

to this

(= (fib3 $n)
   (case $n
      ((0 0)
       (1 1)
       ($_ (+ (fib3 (- $n 1)) (fib3 (- $n 2)))))))

is exactly the place where case can be introduced. Although case differs from nested if in MeTTa in a deeper way than in other languages, so it should also be described carefully

from metta-examples.

Iterative variant should be quicker, but in current metta interpreter's state it is quite opposite due to interpreter cashes all calls during evaluation

To me the second variant is quicker. In both minimal MeTTa and Rust interpreter.

It is weird, but you're right. It was quite opposite on the previous metta versions for me. I haven't tested time difference between these two variants after updating metta.

from metta-examples.

@Necr0x0Der Thank you for explanations. One question regarding case - what $_ symbol means? In case of this function:

(= (fib3 $n)
   (case $n
      ((0 0)
       (1 1)
       ($_ (+ (fib3 (- $n 1)) (fib3 (- $n 2)))))))

as I understand for (== $n 0) result will be 0, for (== $n 1) result will be 1, for $_ (everything else?) result will be sum of recursions. Is this symbol $_ applicable only in case of case? Or it has some other use cases?

from metta-examples.

what $_ symbol means?

In MeTTa it is just a normal variable. Name _ is chosen to be familiar to users of other languages where _ means match anything. Keep in mind that if you want to use couple of such variables in same context you need to name it differently: $_ and $__ or $_1.

from metta-examples.

what $_ symbol means?

In MeTTa it is just a normal variable. Name _ is chosen to be familiar to users of other languages where _ means match anything. Keep in mind that if you want to use couple of such variables in same context you need to name it differently: $_ and $__ or $_1.

Thanks, Vitaly.

from metta-examples.