phoist

Another great tool for optimizations is phoist and all hoisted terms.

Hoisting

( source: MDN Docs/Hoisting )

Hoisting refers to the process whereby the interpreter appears to move the declaration of functions, variables or classes to the top of their scope, prior to execution of the code.

You can think of hoisted terms as terms that have been pletted but in the global scope.

So once you use a hoisted term once, each time you re-use it you are adding almost nothing to the script size.

You can create a hoisted term by using the phoist function. This allows you to reuse the term you hoisted as many times as you want.

This makes phoist a great tool if you need to develop a library for plu-ts; because is likely your functions will be used a lot.

Let's say we wanted to create a library for math functions. We definitely want to have a way to calculate factorials; we already defined pfactorial while introducing recursion, however that definition is not great if we need to re-use it a lot because the term is always inlined.

But now we know how to fix it:

const pfactorial = 
    phoist( precursive(

        pfn([
            lam( int, int ),
            int
        ],  int)
        
        (( self, n ) =>
            pif( int ).$(
                n.ltEq( 1 )
            )
            .then( 1 )
            .else(
                self.$( n.sub( 1 ) )
                .mult( n )
            )
        )

    ))

If you compare this definition with the previous one you'll see that nothing has changed except for the phoist, that's it; now we can use pfactorial as many times we want.

Can I use phoist everywhere?

No

phoist only accepts closed terms (aka. Terms that do not contain external variables); if you pass a term that is not closed to phoist it throws a BasePlutsError error.

So things like:

const fancyTerm = plam( int, int )
    ( n => 
        phoist( n.mult( 2 ) ); // error.
    )

will throw at compilation time because the variable n comes from outside the phoist function. Hence the term is open (not closed).