#!/usr/local/bin/ised --f
@0{0 1 0 2 0 2 0 1 0}; #! F to F+F-F-F+F
@1{1};                 #! + to +
@2{2};                 #! - to -
@10{$$$$$$0};          #! 6 iterations of the system, starting with F ($0)

#! $10 is already the result we wanted.
#! However, to draw the curve, we must simulate turtle graphics
@11{ {0 1 -1}_$10 };   #! F means forward, + means left (1=90 degrees), - means right (-1=-90 degrees)
@12(0 $11 -1);         #! cumulative of angle changes gives absolute orientations
#! x cumulative: {1 0 -1 0} are x increments for each of the 4 possible directions
@13(0 {1 0 -1 0}_$12 -1); #! cyclic nature of _ operator automatically maps the absolute orientations to interval [0 3]
#! y cumulative: {0 1 0 -1} are y increments for each of the 4 possible directions
@14(0 {0 1 0 -1}_$12 -1);
--t '$13;$14' #! output the result