propeller.problems.PSB2.square-digits

===========  PROBLEM DESCRIPTION  =========================
SQUARE DIGITS from PSB2
Given a positive integer, square each
digit and concatenate the squares into a returned string.

Source: https://arxiv.org/pdf/2106.06086.pdf
============================================================

-main

(-main & args)
Runs propel-gp, giving it a map of arguments.

error-function

(error-function argmap data individual)
Finds the behaviors and errors of an individual: Error is 0 if the value and
the program's selected behavior match, or 1 if they differ, or 1000000 if no
behavior is produced. The behavior is here defined as the final top item on
the STRING stack.

instructions

stack-specific instructions, input instructions, close, and constants

random-int

(random-int)
Random integer between -100 and 100

train-and-test-data