18 March 2014
We propose a programming model where effects are treated in a disciplined way,
and where the potential side-effects of a function are apparent in its type
signature. The type and effect of expressions can also be inferred
automatically, and we describe a polymorphic type inference system based on
Hindley-Milner style inference. A novel feature is that we support polymorphic
effects through row-polymorphism using duplicate labels. Moreover, we show
that our effects are not just syntactic labels but have a deep semantic
connection to the program. For example, if an expression can be typed without
an exn effect, then it will never throw an unhandled exception. Similar to
Haskell's `runST` we show how we can safely encapsulate stateful operations.
Through the state effect, we can also safely combine state with let-polymorphism
without needing either imperative type variables or a syntactic
value restriction. Finally, our system is implemented fully in a new language
called Koka and has been used successfully on various small to medium-sized
sample programs ranging from a Markdown processor to a tier-splitted
chat application. You can try out Koka live at http://www.rise4fun.com/koka/tutorial.
|Published in||Mathematically Structured Functional Programming 2014|
Creative Commons Attribution
Daan Leijen. Koka: Programming with Row-Polymorphic Effect Types, 28 August 2013.