42 lines
1.3 KiB
Forth
42 lines
1.3 KiB
Forth
# Accumulator
|
|
|
|
## Description
|
|
|
|
This implements a function that takes an initial value and constructs a new function that returns the value before incrementing the stored value by 1.
|
|
|
|
So, given an initial value of 1, the first time the function is called, 1 is returned. The second, 2, and so on.
|
|
|
|
In traditional Forth, this would be done using a CREATE/DOES> construct. RETRO allows for something similar using the `does` combinator.
|
|
|
|
An example in a traditional Forth:
|
|
|
|
: acc ( n "name" -- )
|
|
create , does> dup >r @ dup 1+ r> ! ;
|
|
|
|
In RETRO, we could begin by rewriting this using the RETRO words:
|
|
|
|
:acc (ns-)
|
|
d:create , [ dup push fetch n:inc pop store ] does ;
|
|
|
|
The `dup push ... pop` pattern is the `sip` combinator, so we can simplify it:
|
|
|
|
:acc (ns-)
|
|
d:create , [ [ fetch n:inc ] sip store ] does ;
|
|
|
|
This is better, but not quite done. RETRO has a `v:inc` for incrementing variables, which would eliminate the n:inc and store. And a `bi` combinator to run two quotes against a value. So we could simplify yet again, resulting in:
|
|
|
|
~~~
|
|
:acc (ns-)
|
|
d:create , [ [ fetch ] [ v:inc ] bi ] does ;
|
|
~~~
|
|
|
|
This removes the primitive stack shuffling, and leaves something that expresses the intent more clearly.
|
|
|
|
Finally, here's a little test case:
|
|
|
|
```
|
|
#10 'foo acc
|
|
foo
|
|
foo
|
|
foo
|
|
```
|