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############################################################################
#
# File: miu.icn
#
# Subject: Program to generate strings from MIU system
#
# Author: Cary A. Coutant, modified by Ralph E. Griswold
#
# Date: January 3, 1994
#
############################################################################
#
# This file is in the public domain.
#
############################################################################
#
# This program generates strings from the MIU string system.
#
# The number of generations is determined by the command-line argument.
# The default is 7.
#
# Reference:
#
# Godel, Escher, and Bach: an Eternal Golden Braid, Douglas R.
# Hofstadter, Basic Books, 1979. pp. 33-36.
#
############################################################################
procedure main(arg)
local count, gen, limit
limit := integer(arg[1]) | 7
gen := set(["MI"])
every count := 1 to limit do {
gen := nextgen(gen)
show(count,gen)
}
end
# show - show a generation of strings
procedure show(count,gen)
write("Generation #",count,", ",*gen," strings")
every write(" ",image(!sort(gen)))
write()
end
# nextgen - given a generation of strings, compute the next generation
procedure nextgen(gen)
local new
new := set()
every insert(new,apply(!gen))
return new
end
# apply - produce all strings derivable from s in a single rule application
procedure apply(s)
# Here's a case where referring to the subject by name inside scanning
# is justified.
s ? {
if ="M" then suspend s || tab(0)
tab(-1) # to last character
if ="I" then suspend s || "U"
tab(1) # back to the beginning
suspend tab(find("III")) || (move(3) & "U") || tab(0)
tab(1) # back to the beginning
suspend tab(find("UU")) || (move(2) & tab(0))
}
end
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