Flatten/Unflatten arrays

Hi all, In Perl there is a way to flatten an array into a string, and a matching function to unflatten the array. This is different from explode/implode because the function supports multidimentional arrays as well. The purpose is to be able to write an array to a flatfile, and when necessary, read it in and it's in it's original form ready to use. Are there PHP functions which do the same thing? If not, has anyone ever written functions to do this? Thanks! Lewis