Pure
pure is a constructor or operation that places a value in a computational context without adding domain-specific effects.
Learn Haskell by Example
pure injects a value into an Applicative context without consuming input or otherwise adding an operation-specific effect.
- How it is used
- Lifts functions or values into an Applicative context so wrapped computations can be composed with `(<*>)`.
- How deep it goes
- Defines `pure` by type and behavior, then implements it for `Parser` and relates it to monadic `return`.
- Examples
- Demonstrates `Maybe` values, a lifted three-argument addition, and a parser instance that preserves unconsumed input.
- What you can do after
- Apply it via Applicative operations to combine wrapped values, and use `return` equivalently in monadic parser code.
Functional Design and Architecture: Examples in Haskell
Pure is a value constructor that terminates a free-monad computation and stores the final value to be returned.
- How it is used
- Terminates free-monad computations and supplies the value returned after interpretation.
- How deep it goes
- Explains Pure as a constructor, continuation placeholder, and final chain terminator within recursive free-monad structure.
- Examples
- Uses sandwich construction operations, including startNewSandwich, addComponent, and finishSandwich, as concrete Pure placeholders.
- What you can do after
- Understand how free-monad chaining replaces Pure placeholders and returns the final computation value.
Read how Functional Design and Architecture: Examples in Haskell explains pure →
Related concepts
- value constructorkind of · A value constructor is a constructor that creates a value of an algebraic data type and may expose part of its representation.
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