Example with @predicate

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Example with @predicate#

Custom predicates allow you to encapsulate reusable boolean logic that can be used inside queries. They can be any Python functions decorated with @predicate, or a dataclass that inherits from Predicate class in EQL. These two become symbolic variables when used within symbolic_mode().

Example Usage#

from dataclasses import dataclass
from typing_extensions import List

from entity_query_language import entity, let, an, predicate, symbolic_mode, symbol, Predicate


@symbol
@dataclass
class Body:
    name: str


@dataclass
class Handle(Body):
    pass


@dataclass
class Container(Body):
    pass

@symbol
@dataclass
class World:
    id_: int
    bodies: List[Body]


# Define a reusable predicate: returns True if a body is a handle by name convention
@predicate
def is_handle(body_: Body) -> bool:
    return body_.name.startswith("Handle")

@dataclass
class HasThreeInItsName(Predicate):
    body: Body

    def __call__(self):
        return '3' in self.body.name


# Sample world containing containers and handles
world = World(
    1,
    [
        Container("Container1"),
        Container("Container2"),
        Handle("Handle1"),
        Handle("Handle2"),
        Handle("Handle3"),
    ],
)

# Build the query using the predicate inside symbolic mode
with symbolic_mode():
    query = an(
        entity(
            body := let(type_=Body, domain=world.bodies),
            is_handle(body_=body),  # use the predicate just like any other condition
            HasThreeInItsName(body)
        )
    )

# Evaluate and inspect the results
results = list(query.evaluate())
assert len(results) == 1
assert isinstance(results[0], Handle)
assert results[0].name == "Handle3"

Notes:

  • The @predicate decorator enables the function to participate in symbolic analysis when used under symbolic_mode().

  • The Predicate class is a dataclass used to define custom predicates by implementing the __call__ method.

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