#!/usr/bin/python3
"""Yield a morphic word for Niedermeier, Reinhardt, and Sander’s H-indexing.

This uses the conventional L-system turtle-graphics commands: f to
draw forward and + and - to turn left and right.  It only draws a
single triangle of the H-index curve.

Example output with fold -w 70:

    afffb-f-fb+f+aafffb-f-fb+f+afffb+f+af-f-afffb-f-fb+f+af-f-afffb+f+afff
    b-f-fb+f+aafffb-f-fb+f+afffb+f+af-f-afffb-f-fb+f+af-f-afffb+f+afffb-f-
    fb+f+a+f+b+f+af-f-afffb+f+afffb-f-fb+f+af-f-afffb-f-fb+f+afffb+f+af-f-
    afffbf-f-b+f+af-f-afffb+f+afffb-f-fb+f+af-f-afffb-f-fb+f+afffb+f+af-f-
    afffbfffafffb-f-fb+f+afffb+f+af-f-afffb-f-fb+f+af-f-afffb+f+afffb-f-fb
    +f+aafffb-f-fb+f+afffb+f+af-f-afffb-f-fb+f+af-f-afffb+f+afffb-f-fb+f+a
    +f+b+f+af-f-afffb+f+afffb-f-fb+f+af-f-afffb-f-fb+f+afffb+f+af-f-afffbf
    -f-b+f+af-f-afffb+f+afffb-f-fb+f+af-f-afffb-f-fb+f+afffb+f+af-f-afffbf
    ffafffb-f-fb+f+afffb+f+af-f-afffb-f-fb+f+af-f-afffb+f+afffb-f-fb+f+aff
    fb+f+af-f-afffb+f+afffb-f-fb+f+af-f-afffb-f-fb+f+afffb+f+af-f-afffbfff
    afffb-f-fb+f+afffb+f+af-f-afffb-f-fb+f+af-f-afffb+f+afffb-f-fb+f+a-f-f
    afffb-f-fb+f+afffb+f+af-f-afffb-f-fb+f+af-f-afffb+f+afffb-f-fb+f+a+f+b
    +f+af-f-afffb+f+afffb-f-fb+f+af-f-afffb-f-fb+f+afffb+f+af-f-afffb-f-fb
    +f+af-f-afffb+f+afffb-f-fb+f+af-f-afffb-f-fb+f+afffb+f+af-f-afffbfffaf
    ffb-f-fb+f+afffb+f+af-f-afffb-f-fb+f+af-f-afffb+f+afffb-f-fb+f+a-f-faf
    ffb-f-fb+f+afffb+f+af-f-afffb-f-fb+f+af-f-afffb+f+afffb-f-fb+f+a+f+b+f
    +af-f-afffb+f+afffb-f-fb+f+af-f-afffb-f-fb+f+afffb+f+af-f-afffb+f+afff
    b-f-fb+f+afffb+f+af-f-afffb-f-fb+f+af-f-afffb+f+afffb-f-fb+f+a+f+b+f+a
    f-f-afffb+f+afffb-f-fb+f+af-f-afffb-f-fb+f+afffb+f+af-f-afffbf-f-b+f+a
    f-f-afffb+f+afffb-f-fb+f+af-f-afffb-f-fb+f+afffb+f+af-f-afffbfffafffb-

"""

def hcurve():
    """Yield a morphic word for Niedermeier, Reinhardt, and Sander’s H-indexing

    These are strings of turtle-graphics commands from an L-system by
    oneearedrabbit.net which draw a single triangle of the H-index
    curve, bottom-up.  The morphic word is by definition infinite.

    """

    queue = ['a'], []
    d = dict(a='afffb-f-fb+f+a', b='b+f+af-f-afffb')
    while True:
        for item in queue[0]:
            for c in item:
                n = d.get(c, c)
                yield n
                queue[1].append(n)
        queue = queue[1][::-1], queue[0]  # amortized constant time
        queue[1].clear()

if __name__ == '__main__':
    for c in hcurve():
        print(c, end='')