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We have a for loop now.

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Chris Pressey 2018-03-14 16:45:35 +00:00
parent 96fbe03ce7
commit ed917566ea
2 changed files with 3 additions and 31 deletions
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HISTORY.md
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@ -4,6 +4,8 @@ History of SixtyPical
0.14 0.14
---- ----
* Added the so-called "open-faced `for` loop", which spans a loop
variable over a range, the end of which is fixed.
* `--origin` and `--output-format` options added to reference compiler. * `--origin` and `--output-format` options added to reference compiler.
* "Tail position" is now more correctly determined for the purposes of * "Tail position" is now more correctly determined for the purposes of
insisting that `goto` only appears in it. insisting that `goto` only appears in it.

32
README.md
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@ -67,37 +67,6 @@ Documentation
TODO TODO
---- ----
### `for`-like loop
We have range-checking in the abstract analysis now, but we lack practical ways
to use it.
We can `and` a value to ensure it is within a certain range. However, in the 6502
ISA the only register you can `and` is `A`, while loops are done with `X` or `Y`.
Insisting this as the way to do it would result in a lot of `TXA`s and `TAX`s.
What would be better is a dedicated `for` loop, like
for x in 0 to 15 {
// in here, we know the range of x is exactly 0-15 inclusive
// also in here: we are disallowed from changing x
}
However, this is slightly restrictive, and hides a lot.
However however, options which do not hide a lot, require a lot of looking at
(to ensure: did you increment the loop variable? only once? etc.)
The leading compromise so far is an "open-faced for loop", like
ld x, 15
for x downto 0 {
// same as above
}
This makes it a little more explicit, at least, even though the loop
decrementation is still hidden.
### Save registers on stack ### Save registers on stack
This preserves them, so that, semantically, they can be used later even though they This preserves them, so that, semantically, they can be used later even though they
@ -123,5 +92,6 @@ is probably NP-complete. But doing it adequately is probably not that hard.
* Automatic tail-call optimization (could be tricky, w/constraints?) * Automatic tail-call optimization (could be tricky, w/constraints?)
* Possibly `ld x, [ptr] + y`, possibly `st x, [ptr] + y`. * Possibly `ld x, [ptr] + y`, possibly `st x, [ptr] + y`.
* Maybe even `copy [ptra] + y, [ptrb] + y`, which can be compiled to indirect LDA then indirect STA! * Maybe even `copy [ptra] + y, [ptrb] + y`, which can be compiled to indirect LDA then indirect STA!
* Optimize `ld a, z` and `st a, z` to zero-page operations if address of z < 256.
[VICE]: http://vice-emu.sourceforge.net/ [VICE]: http://vice-emu.sourceforge.net/