144 lines
3.1 KiB
Markdown
144 lines
3.1 KiB
Markdown
# Control Flow
|
|
|
|
Control flow in Cagire's Forth comes in two families. The first is compiled syntax — `if/then` and `case` — which the compiler handles directly as branch instructions. The second is quotation words — `?`, `!?`, `ifelse`, `select`, `apply` — which pop `( ... )` quotations from the stack and decide whether to run them. Probability and periodic execution (`chance`, `every`, `bjork`) are covered in the Randomness tutorial.
|
|
|
|
## Branching with if / else / then
|
|
|
|
Push a condition, then `if`. Everything between `if` and `then` runs only when the condition is truthy:
|
|
|
|
```forth
|
|
;; degrade sound if true
|
|
coin if
|
|
7 crush
|
|
then
|
|
sine sound
|
|
c4 note
|
|
1 decay
|
|
.
|
|
```
|
|
|
|
The crush is applied on half the hits. The sound always plays. Add `else` for a two-way split:
|
|
|
|
```forth
|
|
coin if
|
|
c5 note
|
|
else
|
|
c3 note
|
|
then
|
|
saw sound
|
|
0.3 verb
|
|
0.5 decay
|
|
0.6 gain
|
|
.
|
|
```
|
|
|
|
These are compiled directly into branch instructions — they will not appear in the dictionary. This is a "low level" way to use conditionals in Cagire.
|
|
|
|
## Matching with case
|
|
|
|
For matching a value against several options. Cleaner than a chain of `if`s when you have more than two branches:
|
|
|
|
```forth
|
|
1 8 rand 4 mod case
|
|
0 of c3 note endof
|
|
1 of e3 note endof
|
|
2 of g3 note endof
|
|
3 of a3 note endof
|
|
endcase
|
|
tri s
|
|
2 fm 0.99 fmh
|
|
0.6 gain 0.2 chorus
|
|
1 decay
|
|
800 lpf
|
|
.
|
|
```
|
|
|
|
A different root note each time the pattern loops. The last line before `endcase` is the default — it runs when no `of` matched:
|
|
|
|
```forth
|
|
iter 3 mod case
|
|
0 of 0.9 gain endof
|
|
0.4 gain
|
|
endcase
|
|
saw s
|
|
.5 decay
|
|
c4 note
|
|
.
|
|
```
|
|
|
|
Like `if/then`, `case` is compiled syntax and does not appear in the dictionary.
|
|
|
|
## Quotation Words
|
|
|
|
The remaining control flow words operate on quotations — `( ... )` blocks sitting on the stack. Each word pops one or more quotations and decides whether or how to execute them.
|
|
|
|
### ? and !?
|
|
|
|
`?` executes a quotation if the condition is truthy:
|
|
|
|
```forth
|
|
( 0.4 verb 6 crush ) coin ?
|
|
tri sound 2 fm 0.5 fmh
|
|
c3 note 0.5 gain 2 decay
|
|
.
|
|
```
|
|
|
|
Reverb on half the hits. `!?` is the opposite — executes when falsy:
|
|
|
|
```forth
|
|
( 0.5 delay 0.9 delayfeedback ) coin !?
|
|
saw sound
|
|
c4 note
|
|
500 lpf
|
|
0.5 decay
|
|
0.5 gain
|
|
.
|
|
```
|
|
|
|
Quiet on half the hits. These pair well with `chance` and `fill` from the Randomness tutorial.
|
|
|
|
### ifelse
|
|
|
|
Two quotations, one condition. The true branch comes first:
|
|
|
|
```forth
|
|
( c3 note ) ( c5 note ) coin ifelse
|
|
saw sound 0.3 verb
|
|
0.5 decay 0.6 gain
|
|
.
|
|
```
|
|
|
|
Reads naturally: "c3 or c5, depending on the coin."
|
|
|
|
```forth
|
|
( 0.8 gain ) ( 0.3 gain ) fill ifelse
|
|
tri s c4 note 0.2 decay .
|
|
```
|
|
|
|
Loud during fills, quiet otherwise.
|
|
|
|
### select
|
|
|
|
Choose the nth quotation from a list. The index is 0-based:
|
|
|
|
```forth
|
|
( c4 ) ( e4 ) ( g4 ) ( b4 ) 0 3 rand select
|
|
note sine s 0.5 decay .
|
|
```
|
|
|
|
Four notes of a major seventh chord picked randomly. Note that this is unnecessarily complex :)
|
|
|
|
### apply
|
|
|
|
When you have a quotation and want to execute it unconditionally:
|
|
|
|
```forth
|
|
( dup + ) apply
|
|
```
|
|
|
|
Pops the quotation and runs it. Simpler than `?` when there is no condition to check.
|
|
|
|
## More!
|
|
|
|
For probability gates, periodic execution, and euclidean rhythms, see the Randomness tutorial. For generators and ranges, see the Generators tutorial.
|