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Normalizes Tensor ranks for use in if conditions.

This enables dry-runs of programs with control flow. Usage: Program the conditions of if statements and while loops to have a batch dimension, and then wrap them with this function. Example:

ctx = frontend.Context
truthy = frontend.truthy

def my_abs(x):
  if truthy(x > 0):
    return x
    return -x

my_abs([-5], dry_run=True)
# returns [5] in Eager mode

This is necessary because auto-batched programs still have a leading batch dimension (of size 1) even in dry-run mode, and a Tensor of shape [1] is not acceptable as the condition to an if or while. However, the leading dimension is critical during batched execution; so conditions of ifs need to have rank 1 if running batched and rank 0 if running unbatched (i.e., dry-run). The truthy function arranges for this be happen (by detecting whether it is in dry-run mode or not).

If you missed a spot where you should have used truthy, the error message will say Non-scalar tensor <Tensor ...> cannot be converted to boolean.

x A Tensor.

x The Tensor x if we are in batch mode, or if the shape of x is anything other than [1]. Otherwise returns the single scalar in x as a Tensor of scalar shape (which is acceptable in the conditions of if and while statements.