I do not know anything about Scheme, but I have to modify someone's program to enable file handling. Is there a way a scheme program can keep checking for the presence of a file (that does not exist), and stop this loop when it finds the text file. During this time gap (until it finds the file), the scheme code should not do anything else. After finding the text file, it can then read the numbers in from this text file.
This is actually a scheme program that contains a GA, and I have my C program that periodically spits the distance moved by a robot onto a text file. This text file is the input for this scheme program and if the text file is created with this distance moved, then the scheme code can use it to run the GA and learn.