ANN: Dogelog Runtime, Prolog to the Moon (2021)

[Greg Ewing]

On 16/09/21 6:56 am, Mostowski Collapse wrote:
> What could be slow, repeatedly requesting the "args"
> field. Maybe I should do:
> 
> help = term.args
> i = 0
> while i < len(help) - 1:
> ____mark_term(help[i])
> ____i += 1
> term = help[i]

Yes, that will certainly help.

But you're still evaluating len(help) - 1 every time around
the loop, so this is even better:

help = term.args
n = len(help) - 1
i = 0
while i < n:
     mark_term(help[i])
     i += 1
term = help[i]

Some general principles to be aware of:

* Almost nothing is free -- Python very literally does what
you tell it to do, even if it looks dumb.

* Access to attributes and global variables is expensive
(requires at least one dict lookup, often more in the case
of attributes).

* Access to *local* variables, on the other hand, is very
cheap (essentially an array lookup).

* Function calls are expensive -- both to look up the name, if
it's global, which it usually is, and the machinery of the
call itself.

* Creating objects is expensive. Creating instances of
user-defined objects is more expensive than built-in ones.

-- 
Greg