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############################################################################
#
# File: parens.icn
#
# Subject: Program to produce random balanced strings
#
# Author: Ralph E. Griswold
#
# Date: March 26, 2002
#
############################################################################
#
# This file is in the public domain.
#
############################################################################
#
# This program produces parenthesis-balanced strings in which
# the parentheses are randomly distributed.
#
# Options: The following options are available:
#
# -b n Bound the length of the strings to n left and right
# parentheses each. The default is 10.
#
# -n n Produce n strings. The default is 10.
#
# -l s Use the string s for the left parenthesis. The default
# is ( .
#
# -r s Use the string s for the right parenthesis. The default
# is ) .
#
# -v Randomly vary the length of the strings between 0 and
# the bound. In the absence of this option, all strings
# are the exactly as long as the specified bound.
#
# For example, the output for
#
# parens -v -b 4 -l "begin " -r "end "
#
# is
#
# begin end
# begin end begin end
# begin begin end end begin end
# begin end begin begin end end
# begin end
# begin begin end end
# begin begin begin end end end
# begin end begin begin end end
# begin end begin end
# begin begin end begin end begin end end
#
#
# Comments: This program was motivated by the need for test data
# for error repair schemes for block-structured programming lan-
# guages. A useful extension to this program would be some
# way of generating other text among the parentheses. In addition
# to the intended use of the program, it can produce a variety of
# interesting patterns, depending on the strings specified by -l
# and -r.
#
############################################################################
#
# Links: options, random
#
############################################################################
link options
link random
global r, k, lp, rp
procedure main(args)
local string, i, s, bound, limit, varying, opts
randomize()
bound := limit := 10 # default bound and limit
lp := "(" # default left paren
rp := ")" # default right paren
opts := options(args,"l:r:vb+n+")
bound := \opts["b"] | 10
limit := \opts["n"] | 10
lp := \opts["l"] | "("
rp := \opts["r"] | ")"
varying := opts["v"]
every 1 to limit do {
if \varying then k := 2 * ?bound else k := 2 * bound
string := ""
r := 0
while k ~= r do {
if r = 0 then string ||:= Open()
else if ?0 < probClose()
then string ||:= Close() else string ||:= Open()
}
while k > 0 do string ||:= Close()
write(string)
}
end
procedure Open()
r +:= 1
k -:= 1
return lp
end
procedure Close()
r -:= 1
k -:= 1
return rp
end
procedure probClose()
return ((r * (r + k + 2)) / (2.0 * k * (r + 1)))
end
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