study 03 of 10

Decisions and loops

You have already used two words that end with a colon: l 1 16: and if c:. They are modifiers: they decide whether, how often, or with which chance the rest of the line runs. This study goes through all of them and builds a drum fill: a snare roll that thickens towards the end of the bar.

A modifier, then a line or a block

A modifier ends with :. What it governs is either the rest of the same line, or, when nothing follows the colon, the indented lines below it:

Listing 3-1 · The same loop, in one line and as a block

def two_forms
  menu "LEARN" >> "TWO FORMS"
  l 1 4: tr.add i
  l 9 12:
    tr.add i
    pl.set i amp.vol 100

A block ends at the first line that is less indented. All the lines of one block must start at the same column; the width is yours to choose, but only spaces count (a tab is an error). Modifiers also chain on one line, read from left to right: l 1 16: if er 5 16 i: tr.add i is a loop, then a condition, then the action.

`if`, `elif`, `else`

if c: runs what it governs when c is true. elif c: (else if) and else: follow it, on the next lines and at the same indentation; only the first branch whose condition holds runs.

Listing 3-2 · Three cases for each step

def kick_snare_hat
  menu "LEARN" >> "K S H"
  tr.clr
  l 1 16:
    tr.add i
    if eq mod i 8 1: pl.set i amp.vol 127
    elif eq mod i 8 5: pl.set i amp.vol 110
    else: pl.set i amp.vol 50

Output · what the simulator prints for $ otype.py run kick_snare_hat -v

kick_snare_hat  seed 1 (--seed)  pattern A01 len 16 (default)  track 1
T1  1   5   9   13
    XXXXXXXXXXXXXXXX
    step 1: amp.vol 127   step 2: amp.vol 50   step 3: amp.vol 50   step 4: amp.vol 50
    step 5: amp.vol 110   step 6: amp.vol 50   step 7: amp.vol 50   step 8: amp.vol 50
    step 9: amp.vol 127   step 10: amp.vol 50   step 11: amp.vol 50   step 12: amp.vol 50
    step 13: amp.vol 110   step 14: amp.vol 50   step 15: amp.vol 50   step 16: amp.vol 50
      X trig  ! one-shot  o trigless trig  - trigless lock  l locks only  . none
part:  tempo 120
cost: 332/336   random draws: rand 0  toss 0  prob 0  drunk 0  file 0

Loops: `l` and `each`

l a b: counts i from a to b, both included, downwards if a is greater. Its bounds are fixed before the run: numbers, a const, a param, or an argument of your function, but never a variable. That is what lets OType promise that every run ends.

Inside a loop in a loop, i is the inner counter and j the outer one:

Listing 3-3 · Two counters: j the beat, i the step in the beat

def diagonal
  menu "LEARN" >> "DIAGONAL"
  tr.clr
  l 1 4:                                # j: beats 1..4
    l 1 4:                              # i: steps 1..4 of the beat
      if eq i j: tr.add add mul sub j 1 4 i

Output · what the simulator prints for $ otype.py run diagonal

diagonal  seed 1 (--seed)  pattern A01 len 16 (default)  track 1
T1  1   5   9   13
    X....X....X....X
      X trig  ! one-shot  o trigless trig  - trigless lock  l locks only  . none
part:  tempo 120
cost: 172/256   random draws: rand 0  toss 0  prob 0  drunk 0  file 0

The trig moves one step later in each beat: step 1 of the first beat, step 2 of the second, and so on. add mul sub j 1 4 i turns the beat and the step in the beat into a step of the pattern: (j − 1) × 4 + i. Everything after # is a comment.

each: repeats for each step of the current step set, with i as the step. It shines once you narrow the steps to, say, those that hold a trig; that is the subject of tracks and steps.

Leaving early: `break` and `stop`

break leaves the loop it is in; stop ends the whole function there.

Listing 3-4 · Stop placing trigs past step 6

def first_six
  menu "LEARN" >> "FIRST SIX"
  tr.clr
  l 1 16:
    if gt i 6: break
    tr.add i

Output · what the simulator prints for $ otype.py run first_six

first_six  seed 1 (--seed)  pattern A01 len 16 (default)  track 1
T1  1   5   9   13
    XXXXXX..........
      X trig  ! one-shot  o trigless trig  - trigless lock  l locks only  . none
part:  tempo 120
cost: 159/208   random draws: rand 0  toss 0  prob 0  drunk 0  file 0

Chance and counting: `prob`, `every`, `skip`

prob p: runs what it governs with a chance of p percent. Now the fill: the further into the bar, the likelier a snare.

Listing 3-5 · A fill that thickens

def snare_fill
  menu "LEARN" >> "FILL"
  tr.clr
  l 1 16: prob mul i 6: tr.add i

Output · what the simulator prints for $ otype.py run snare_fill --seed 3

snare_fill  seed 3 (--seed)  pattern A01 len 16 (default)  track 1
T1  1   5   9   13
    ...X.XXX.XXX.XXX
      X trig  ! one-shot  o trigless trig  - trigless lock  l locks only  . none
part:  tempo 120
cost: 184/208   random draws: rand 0  toss 0  prob 16  drunk 0  file 0

Each run draws new numbers, so each press gives a different fill. The simulator shows one of them (its --seed fixes which; the randomness study explains seeds).

every n: runs once every n times the line is reached, and skip n: every time except that one. Their count is kept from one press to the next, so every 4: tr.add 16 adds a trig on step 16 on every fourth press only.

What you learned

…:: a modifier governs the rest of its line, or the indented block below
if · elif · else: choose between branches
l a b: · each:: count with i (and j outside) · visit the steps
break · stop: leave the loop · leave the function
prob p:: with p % chance
every n: · skip n:: once every n times · all but that time

Try it

Rewrite first_six without break, with the loop bounds alone.
Make the fill thin out instead: a chance of sub 100 mul i 6.
Add an every 2: line that clears the track on every other press.

Decisions and loops

A modifier, then a line or a block

if, elif, else

Loops: l and each

Leaving early: break and stop

Chance and counting: prob, every, skip