Just
Just is a constructor of the Maybe type that represents a present value by wrapping it.
Functional Programming in JavaScript
A Maybe case that wraps a defined value.
- How it is used
- Wraps a present value in Maybe so later steps can keep chaining safely.
- How deep it goes
- Defines the Just subtype and shows its role in mapping and unwrapping, but leaves broader monad theory to later treatment.
- Examples
- Uses student lookup, address extraction, and a simple half function on wrapped numbers.
- What you can do after
- Apply it to keep a successful value in a safe container through chained transformations.
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Learn Haskell by Example
Just is the Maybe constructor that contains a value of a parameterized type.
- How it is used
- Represents present values within optional results, recoverable failures, and associative-list updates.
- How deep it goes
- Explains the constructor, pattern matching, defaults, and update behavior, but does not descend into deeper typeclass machinery.
- Examples
- Uses file-path parsing, fromMaybe defaults, and associative-list insertion, replacement, or deletion.
- What you can do after
- Apply pattern matching and Maybe functions to consume wrapped values without treating missing results as crashes.
Related concepts
- maybe functionpart of · The maybe function eliminates a Maybe value by returning a default for Nothing or applying a handler to the contained value.
- optionuses · An option type is a type that explicitly represents either a value of a specified type or the absence of a value.
- Nothingalternative to · Nothing is a Maybe constructor representing the absence of a contained value or additional failure information.
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