Crate scrapmetal [−] [src]

Scrap Your Boilerplate!

This crate provides the traversing, transforming, and querying helpers and combinators from the Haskell paper "Scrap Your Boilerplate: A Practical Design Pattern for Generic Programming" by Lämmel and Peyton Jones to Rust.

Structs

Everything	Recursively perform a query in a top-down, left-to-right manner across a data structure. The `Q: Query<R>` queries individual values, while the `F: FnMut(R, R) -> R` joins the results of multiple queries into a single result.
Everywhere	Recursively perform a transformation in a bottom up manner across a complete data structure.
EverywhereBut	Recursively perform a transformation in a bottom up manner across a complete data structure.
MutateEverything	Recursively perform a query in a top-down, left-to-right manner across a data structure. The `M: GenericMutate<R>` queries individual values, while the `F: FnMut(R, R) -> R` joins the results of multiple queries into a single result.
Mutation	A mutation creates some value `R` from mutable references to a `U`. It can be called on values of any type `T`, not just on values of type `U`, so it requires a default `R` value for when it is called on values which are not a `T`.
Query	A query non-destructively creates some value `R` from references to a `U`. It can be called on values of any type `T`, not just on values of type `U`, so it requires a default `R` value for when it is called on values which are not a `T`.
Transformation	A transformation takes some value `U` and returns a new, transformed version of it. It can be called on values of any type `T`, not just on values of type `U`, in which case it is simply the identity function.

Traits

GenericMutate	A similar work around as `GenericTransform`, but mutating in place and optionally returning some query type, rather than taking `self` and returning the same `Self` type.
GenericQuery	A similar work around as `GenericTransform`, but returning a query type, rather than the same type. This is roughly equivalent to `for<T> FnMut(&T) -> R`.
GenericTransform	Work around Rust's lack of higher-rank type polymorphism with a trait that has a generic `fn transform<T>` method. Essentially, we'd really prefer taking arguments of type `F: for<T> FnMut(T) -> T` rather than `F: GenericTransform` but Rust doesn't support them yet (ever?).
Term	A `Term` is a value that can be mapped or queried.