A string of braces is considered valid if all braces are matched with the correct brace.

Way too loosly defined in my eyes.
There could be clear rules for the validity of scoping braces:

1. an valid expression starts with the outer scope represented by '(' & ')' and nested scopes are surrounded by '[' & ']' and further nesting by '{' & '}'
2. an expression is invalid if there is no closing partner

This would produce clearer rules and less ambiguity for the kata.
But the current examples are different: "(){}[]" => true
Still the solutions are somewhat taking order of scopes into account, which isnt mentioned in the instructions

so many options for nice pattern matching in haskell but some ppl just want to stick with regrets