Control Structures

Flix — being a functional programming language — has few control-structures. Most control is simply function application. The Flix control structures are:

If-Then-Else: A traditional if-then-else expression.
Pattern Matching: A functional construct for taking apart algebraic data types.
Foreach: An imperative construct for iteration through collections.
Foreach-Yield: An imperative construct for building new collections from existing collections.
Monadic For-Yield: A functional construct for monadic operations, similar to Scala's for-comprehensions and Haskell's do-notation.
Applicative For-Yield: A functional construct for applicative operations, similar to Haskell's applicative do-notation.

What's the difference between foreach, foreach-yield, monadic forM, and applicative forA?:

The following table gives some uses cases for each construct:

Action	Construct
Print all elements in a collection.	Foreach
Apply an effectful operation to each element in a collection.	Foreach
Build a new collection from existing collections.	Foreach-Yield
Transform the elements of a collection.	Foreach-Yield
Convert a collection of one type into another type.	Foreach-Yield
Work with `Option`s and `Result`s.	Monadic For-Yield
`flatMap` through a `Monad`.	Monadic For-Yield
Work with `Validation`s	Applicative For-Yield

Note: Flix does not have traditional while or for-loops. Instead, we recommend the use recursion and/or one of the above constructs.

Programming Flix

Control Structures