Semigroup

funstruct.typeclasses.semigroup

Semigroup: an associative binary combine operation over a type.

Law: combine(combine(a, b), c) == combine(a, combine(b, c))

Unlike a Protocol/ABC, this is a value — you can have multiple Semigroup instances for the same type (e.g. int under + vs int under *).

When to use

Any time you need to combine/merge two values of the same type and the operation is associative (grouping doesn't matter).

Business examples

• Merging configs: combine(default_config, user_config)
• Error accumulation in Validated: combine error lists
• Merging frozendicts: right-biased key merge
• Combining log entries: concatenate CList of events
• Non-empty collections: concat where empty isn't meaningful

Semigroup dataclass

An associative binary operation over a type.

Source code in funstruct/typeclasses/semigroup.py

@dataclass(frozen=True)
class Semigroup:
    """An associative binary operation over a type."""

    typ: type
    combine: Callable