pattern-matching

Understand how Idris' type checker handles pattern matching on existential types like EqNat. Learn why replacing Just (Same _) with Just _ causes type mismatch errors, even with single constructors, and how to refine dependent goals properly.

Fast, idiomatic ways to check if a string contains a substring in Bash. Use [[ *substring* ]], case, or =~ for regex. Also covers quoting and portability.