Augmenting Dynamic Typing with Static-Analysis

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Augmenting Dynamic Typing with Static-Analysis Reid Draper @reiddraper

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Reid Draper @reiddraper

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takeaways

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tl;dr

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JUST USE HASKELL

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JUST USE IDRIS

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several modern functional languages have optional type systems

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they are mature enough to be useful

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they find real bugs

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and improve documentation

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with some work, you can integrate them into your CI system

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motivation

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%% Return a list of locators, in our case, we'll use cluster names %% that were saved in the ring cluster_mgr_sites_fun() -> %% get cluster names from cluster manager Ring = riak_core_ring_manager:get_my_ring(), Clusters = riak_repl_ring:get_clusters(Ring), [{?CLUSTER_NAME_LOCATOR_TYPE, Name} || {Name, _Addrs} <- Clusters].

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static-typing has many benefits

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prevents many errors during compile-time

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enhanced documentation

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%% @doc Return a list of all manifests in the %% `active' or `writing' state active_and_writing_manifests(Dict) -> orddict:to_list(filter_manifests_by_state(Dict, [active, writing])).

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%% @doc Return a list of all manifests in the %% `active' or `writing' state -spec active_and_writing_manifests(orddict:orddict()) -> [{binary(), lfs_manifest()}]. active_and_writing_manifests(Dict) -> orddict:to_list(filter_manifests_by_state(Dict, [active, writing])).

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-spec f(orddict:orddict()) -> [{binary(), lfs_manifest()}]. !

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a guide for structuring programs

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(potentially) better performance

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there are many popular dynamically-typed languages in industry

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JavaScript Java PHP C# Python! C++ Ruby C Objective-C CSS Perl Shell Scala Haskell R Matlab Clojure CoffeeScript Visual Basic Groovy http://redmonk.com/sogrady/2014/01/22/language-rankings-1-14/

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so what do we do?

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can we add a type-system?

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Retrofitting a type system into a language not designed with typechecking in mind can be tricky; ideally, language design should go hand-in-hand with type system design. Benjamin C. Pierce, Types and Programming Languages p. 9

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history

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an incomplete and likely wrong history

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adding dynamic types to a statically-typed language 1989 M. Abadi, L. Cardelli, B. Pierce, G. Plotkin, statically-typed language

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Cartwright and Fagan introduce Soft-Typing 1991 Robert Cartwright, Mike Fagan,

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"The key concept of soft typing is that a type checker need not reject programs containing statically 'ill typed' phrases" 1991 Robert Cartwright, Mike Fagan,

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Soft-Types implemented with Scheme 1994 Andrew K. Wright , Robert Cartwright,

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Marlow and Wadler add static- types to Erlang* 1997 * with some caveats… Andrew K. Wright , Robert Cartwright,

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Bracha introduces optional types in Pluggable Type Systems 2004 Gilad Bracha,

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"In contrast, optional type systems are neither syntactically nor semantically required, and have no effect on the dynamic semantics of the language." 2004 Gilad Bracha,

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Erlang's Dialyzer becomes viable 2006 Lindahl, Sagonas,

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overcomes many of the issues Marlow and Wadler had 2004 Lindahl, Sagonas,

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Gradual typing for functional languages 2006 Siek, Taha,

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The design and implementation of typed scheme 2008 now called Typed Racket Tobin-Hochstadt, Felleisen,

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inspiration for typed Clojure 2008 Tobin-Hochstadt, Felleisen,

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introduces Occurrence typing 2008 Tobin-Hochstadt, Felleisen,

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(: flexible-length (-> (U String (Listof Any)) Integer)) (define (flexible-length str-or-lst) (if (string? str-or-lst) (string-length str-or-lst) (length str-or-lst)))

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state of the art

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Dialyzer for Erlang

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Typed Racket

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Typed Clojure

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Dart

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Dialyzer at Basho

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we write a distributed database in Erlang: Riak

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correctness and fault-tolerance are import

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bugs are inevitable

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sometimes embarrassing

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avoid preventable bugs

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we use Dialyzer for this

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recently hooked it up with CI

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takeaways

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tl;dr

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several modern functional languages have optional type systems

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they are mature enough to be useful

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they find real bugs

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and improve documentation

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with some work, you can integrate them into your CI system

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Questions? @reiddraper