Infinite loop nested within a block in Ruby - ruby

Question

Here's what I'm trying to do. I'm iterating through an array of strings, each of which may contain [] multiple times. I want to use String#match as many times as necessary to process every occurrence. So I have an Array#each block, and nested within that is an infinite loop that should break only when I run out of matches for a given string.
def follow(c, dir)
case c
when "\\"
dir.rotate!
when "/"
dir.rotate!.map! {|x| -x}
end
return dir
end
def parse(ar)
ar.each_with_index { |s, i|
idx = 0
while true do
t = s.match(/\[[ ]*([a-zA-Z]+)[ ]*\]/) { |m|
idx = m.end 0
r = m[1]
s[m.begin(0)...idx] = " "*m[0].size
a = [i, idx]
dir = [0, 1]
c = ar[a[0]][a[1]]
while !c.nil? do
dir = follow c, dir
ar[a[0]][a[1]] = " "
a[0] += dir[0]; a[1] += dir[1]
c = ar[a[0]][a[1]]
if c == ">" then
ar[a[0]][a[1]+1] = r; c=nil
elsif c == "<" then
ar[a[0]][a[1]-r.size] = r; c=nil
end
end
ar[a[0]][a[1]] = " "
puts ar
}
if t == nil then break; end
end
}
parse File.new("test", "r").to_a
Contents of test:
+--------+----------+-------------+
| Colors | Foods | Countries |
+--------+----------+-------------+
| red | pizza | Switzerland |
/--> /----> | |
| |[kale]/ | hot dogs | Brazil |
| | <----------------------\ |
| | orange |[yellow]\ | [green]/ |
| +--------+--------|-+-------------+
\-------------------/
Goal:
+--------+----------+-------------+
| Colors | Foods | Countries |
+--------+----------+-------------+
| red | pizza | Switzerland |
yellow kale | |
| | hot dogs | Brazil |
| green |
| orange | | |
+--------+-------- -+-------------+
Actual output of program:
+--------+----------+-------------+
| Colors | Foods | Countries |
+--------+----------+-------------+
| red | pizza | Switzerland |
yellow kale | |
| | hot dogs | Brazil |
| <----------------------\ |
| orange | | [green]/ |
+--------+-------- -+-------------+
(Since the array is modified in place, I figure there is no need to update the match index.) The inner loop should run again for each pair of [] I find, but instead I only get one turn per array entry. (It seems that the t=match... bit isn't the problem, but I could be wrong.) How can I fix this?