A file for a “Code Golf” challenge. Specially “Timber”, № 8, here: http://codegolf.stackexchange.com/questions/16707/9-hole-challenge

timber_short.pl

# roosto’s “Code Golf” v3 149 characters
# problem is #8 here: http://codegolf.stackexchange.com/questions/16707/9-hole-challenge
# 
# The basic idea here is to go line by line, looking through the current line for whitespace.
# When we find a whitespace character we see if the character above it needs
# to have a non-whitespace character, a.k.a. a “supporting” character below it.
# If the “supporting” character above the whitespace character is not '/' or '\', a.k.a. a “bracing” character,
# then shit is fucked. We make comparisons easier and severely limit corner cases by
# kinda normalizing the input with a few regexs before we get into it.
# 
# The corner cases are:
#   * uneven line lengths (OK, because undef evaluates to false)
#   * “bracing” characters at the beginning or end of a line (OK, because we pad beginning & end with '0')
#   * “bracing” characters which do not have a “supporting” character on the appropriate side (OK, because we turn these into non-“bracing” characters)
# 
# That last point was the hardest to figure for me. A “bracing” character without a “supporting”
# character on its appropriate side is still a “supporting” character if it has a “supporting”
# character beneath it.
# 
# Improvements? I think the way that true or false is printed could be made shorter
#

$0="tru";
if ( 0 ) {
	open F,pop; # bareword 'F' is now a file pointer to file named by ARGV[0]
	while(<F>){ # line by line, contents of line stored as a string in $_
		y/0/6/; # transliterate '0' -> '6'
		s/^|\s|$/0/g; # all whitespace into '0', also pad the beginning & end of the line with '0' (pad end of line is in case of file not ending in newline)
		s#\\(?=0)|(?<=0)/|[^\\/0]#6#g; # '\' followed by '0' & '/' preceded by '0' into '6', anything not '/', '\', or '0' into '6'
		@n=split //; # transform $_ into an array, one element for each char
		for(0..@n){ # quick & _quite_ dirty version of: for( $_ = 0; $_ < last index of @n; $_++ )
			if(!$n[$_] && $l[$_]==6){ # in the “minified” version this if is a ternary to save characters–#sorrynotsorry (no, but really it’s gross [but really that’s what this is all about])
				# if current character is 0; i.e., whitespace in original file && the character above it is not / or \, we are unstable
				# keep in mind that we converted any '/' or '\' w/o its “supporting” char next to it to a '6' …
				# a '/' or '\' w/o a “supporting” char next to it is still supported if a “supporting” char is below it
				$0='fals' # no need for a semicolon for the last statement in a block! a 1 character savings! (I am a terrible person)
				# we could `exit 1` here, but `exit 1;`; is 7 characters, no to mention the `print`…
				# Why sacrifice character count in exchange for an efficiently running program? (I work on crux all day—I’ve earned this, OK.)
			}
		}
		@l=@n; # save this line, so as we have the line above the next line to compare to
	}
	print "$0e\n"; # print return value
}

# $ tail -2 true | wc -c
#      147

$0=tru;open F,pop;while(<F>){y/0/6/;s/^|\s|$/0/g;s!\\(?=0)|(?<=0)/|[^\\/0]!6!g;@n=split//;for(0..@n){!$n[$_]&&$l[$_]==6?$0=fals:1}@l=@n}print"$0e
"

hehe … That super gross minified Perl seems to be upsetting github’s Perl syntax highlighter. The / at the end of the first regex is marked as red.