For Linux:(tried and checked in ubuntu)
To add SPL and APL syntax highlighting in vim
Copy apl.vim and spl.vim into $HOME/.vim/syntax/(create if any of these doesnt exist).
Open $HOME/.vimrc and add the following lines:
set nocompatible
syntax on
autocmd BufRead,BufNewFile *.spl set filetype=spl
autocmd BufRead,BufNewFile *.apl set filetype=apl
Close any vim sessions and re-open.