Much easier way to write control flows

[chaoming0625]

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• Describe your goal, and if possible provide a code snippet with a motivating example.

Control flow is not easy in BrainPy because it relies on JAX. I think maybe there is a more conveninet way to write control flows. Like,

import brainpy as bp
import brainpy.math as bm

def f(a)
  return bm.ifelse(a > 10., lambda x: 10., 
                   a > 5 and a <= 10, lambda x: x*2,
                   lambda x: x+2, x)

Or,

def f(b)
  return bm.ifelse(conditions=[a > 10.,  a > 5 and a <= 10], 
                   functions=[lambda x: 10., lambda x: x*2, lambda x: x+2], 
                   operands=x,
                   dyn_vars=...)

[chaoming0625]

#189