Documentation

Unsafe head function with descriptive error message.

This function is partial and will throw an error on empty lists. It should only be used when there's a strong invariant guaranteeing the list is non-empty.

Why use this instead of a total function?

• Preserves existing type signatures and caller simplicity
• Makes invariant violations fail fast with clear error messages
• Avoids pushing complexity up the call chain for conditions that should never occur
• Used specifically in getGenerators where groupBy never produces empty groups

When to use:

• Internal functions with strong invariants
• Performance-critical code where the invariant is guaranteed
• When converting to total functions would complicate the entire call chain

When NOT to use:

• Public APIs where callers might pass invalid input
• When the input domain genuinely includes edge cases
• When safety is more important than performance