#
# This file shows an answer to the opening exercise, total_margin,
# and then evolves that code into a functional solution.
#

games = [ [102, 51], [78, 67], [53, 94], [64, 75], [54, 71], [64, 68] ]

# imperative solution

total_margin = 0
for p in games:
    difference = abs(p[0]-p[1])
    total_margin += difference 

# examine the loop

total_margin = 0
for p in games:
    difference = abs(p[0]-p[1])     # 1. do something with p
    total_margin += difference      # 2. accumulate result from #1

# separate this into two loops

# ---------------------------------------------------------------
# in loop 1, change "do something with result" to *record* result

results = []
for p in games:
    difference = abs(p[0]-p[1])    # 1. do something with p
    results.append(difference)     # 2. record result from #1

# then factor "do something with p" into a function

def margin_for(two_list):
    return abs(two_list[0]-two_list[1])

# and use the function

results = []
for p in games:
    difference = margin_for(p)      # 1. do something with p -- in a fxn
    results.append(difference)      # 2. record result from #1

# map does all of this... just give it margin_for()

results = map(margin_for, games)

# map produces a "map object" that we can loop over

# ---------------------------------------------------------------
# now, the second loop adds up the results

total_margin = 0
for r in results:
    total_margin += r               # 1. accumulate result from #1
    
# Python 3 doesn't have a generic reduce function.
# In this case, we can sum a list made from the map:
#
# total_margin = sum(list(results))

# --------------------------------------------------------------
# in Racket, apply does all of this -- as long as you give it +:
#
# (apply + results)