study 08 of 10

Chance you can repeat

Random choices are where scripts surprise you. They are also where you want control: keep the variation you liked, come back to it tomorrow. This study covers OType's random values, its lists, and the seeds that make chance repeatable.

Random values

write	gives
`rnd n`	0 to n − 1
`rrand a b`	a to b, both included
`toss`	0 or 1
`chance p`	1 with p % chance, else 0
`prob p:`	the modifier you know: run the line with p % chance

Lists

A list is a few numbers between braces, up to sixteen: {60 90 127}. Lists are constants, written in the script; usually you name them with const. Three operations read them: pick list (one element at random), at list n (the n-th, from 1) and len list (how many).

Listing 8-1 · Random hats, with volumes from a list

const vols {60 90 127}

def rnd_hats
  menu "LEARN" >> "RND HATS"
  tr.clr
  l 1 16:
    if chance 60:
      tr.add i
      pl.set i amp.vol pick vols

Output · what the simulator prints for $ otype.py run rnd_hats -v --seed 5

rnd_hats  seed 5 (--seed)  pattern A01 len 16 (default)  track 1
T1  1   5   9   13
    ...XXX..XXXXXX.X
    step 4: amp.vol 90   step 5: amp.vol 60   step 6: amp.vol 60   step 9: amp.vol 60
    step 10: amp.vol 90   step 11: amp.vol 60   step 12: amp.vol 90   step 13: amp.vol 60
    step 14: amp.vol 127   step 16: amp.vol 60
      X trig  ! one-shot  o trigless trig  - trigless lock  l locks only  . none
part:  tempo 120
cost: 244/304   random draws: rand 10  toss 16  prob 0  drunk 0  file 0

Some operations draw a value for every step of the context at once: pl.rnd p locks parameter p at random on each trig, smp.rnd a b locks a sample slot between a and b. They save you a loop.

Seeds

Each press draws new numbers. seed n fixes the draws: from that line on, the same n always gives the same results, on the unit as in the simulator. Make the seed a setting, and the player can browse variations and come back to the one they liked:

Listing 8-2 · Variation 1, 2, 3…: each one always the same

def variations
  menu "LEARN" >> "VARIATIONS"
  param pick_no 1 1 99
  seed pick_no
  tr.clr
  l 1 16: prob 40: tr.add i

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

variations  seed 1 (--seed)  pattern A01 len 16 (default)  track 1
T1  1   5   9   13
    ...X...XX.....XX
      X trig  ! one-shot  o trigless trig  - trigless lock  l locks only  . none
part:  tempo 120
cost: 149/193   random draws: rand 0  toss 0  prob 16  drunk 0  file 0

A seed holds until the end of the block it is in; outside it, the draws go on as before. That lets you fix one part of a function and leave the rest free.

Chance in OType comes from five separate streams: one for rnd rrand pick, one for toss chance, one for prob, one for drunk, and one for the files on the card. Adding a prob line therefore does not change what the next rrand gives. seed sets all five; rand.seed, toss.seed, prob.seed, drunk.seed and file.seed set one each.

A/B with a seed

Combine a seed with flip from variables and memory: one press gives variation 7, the next one the pattern without randomness, and so on.

Listing 8-3 · One press a variation, the next the reference

def ab_locks
  menu "LEARN" >> "A/B FX"
  seed ? flip 7 0
  steps has.trig:
    pl.rnd fx1 1

What you learned

rnd · rrand · toss · chance: random values
{…} · pick · at · len: constant lists and their reading
pl.rnd · smp.rnd: a random lock on every trig of the context
seed n: the same draws for the same n, until the end of the block
streams: five independent sources; rand.seed and the others seed one

Try it

Run variations on the computer with --param pick_no=2, then 3: each pattern is always the same.
Put the seed of rnd_hats in a block around the trigs only, so the volumes stay free.
Use at vols rrand 1 3 instead of pick vols. Is it the same?