This document should serve as an introduction into the internals of yabasic. Both are GNU tools and come with their own documentation in info format. With Flex you can define the tokens of yabasic.
Tokens are the keywords which constitute the skeleton of any yabasic program.
The Bison input-file defines the grammar of yabasic. Here are some remarks about how yabasic organises its variables. The variable list for a subroutines is created, as soon as yabasic starts executing a subroutine and it is removed as soon as the subroutine is left. The next time this command is executed, the variable need not be searched again, and access is quite fast. And again, the location of the variable is stored with the command to speed up the next access.