Define an alias to a parametrized command

[Volodymyr Prokopyuk]

Hello,

I'd like to define a shorter alias to a parametrized command. My two
specific use cases are

   - Define \acc { c='8 d e } to be translated into \acciaccatura { c='8 d
   e }
   - Define \af 4. to be translated into \after 4.\!

I've tried the \set command, but it seems that the \set command does not
handle parameters. I have an intuitive understanding that this type of
aliases can be done with Scheme, but I do not know how exactly.

Thank you,
Vlad