Update: I have found a better way. See this post.
So, probably the easiest way (even if somewhat pokey) to wrap a CLI program with a Cocoa GUI is to use AppleScript as the bridge. For example:
do shell script “cd /Xcode_projects/Debug; ./sample > result.txt”
is the contents of a sample applescript, where result.txt is the output of the CLI, sample is the name of the CLI program. One would use NSTask to run the applescript(in order to run the CLI and generate output).