Yes, we want flexibility, but we also strive for safety, hopefully at the right places.
Overview
Minimize surprises
Limiting effects*
In place changes are rare and visible, direct out of context changes are impossible.
Failures and Errors*
We distinct between failure that can normally happen and can be handled, and coder’s error.
Validation dialect*
Validating input or other values is important part and should be visible and explicit.