#!pl0

# [test.pl0] A PL0 example "program"

# first we define a few operation the hard way.

fun add(a,b) = if a = 0 then b else 1 + add(a-1,b)

fun times(a,b) = if a = 0 then 0 else add(times(a-1,b),b)

fun fact(n) 
  = if n = 0 then
      1
    else
      times(n, fact(n-1))

fun profile() = fact(6)

# now try the evaluator with primitive ground expression

run 1
run 1+3
run 2*7-1

# now try the evaluator using functions

run add(0,3)
run add(1,3)
run add(7,3)

run times(7,3)

# following an example for profiling.
# It may take a moment to compute, but
# executes 2839 function calls and
# evaluates a total of 23347 expression.

# on a fast machine, you might want to
# increase the argument slightly to gain
# a visible effect. Then notice that the
# interpreter is not yet optimized for
# speed.

run profile()