Augmenting Dynamic Typing with Static-Analysis Reid Draper - PowerPoint PPT Presentation

Augmenting Dynamic Typing with Static-Analysis Reid Draper @reiddraper

Reid Draper @reiddraper

takeaways

tl;dr

JUST USE HASKELL

JUST USE IDRIS

several modern functional languages have optional type systems

they are mature enough to be useful

they find real bugs

and improve documentation

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

motivation

%% 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].

static-typing has many benefits

prevents many errors during compile-time

enhanced documentation

%% @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])).

%% @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])).

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

a guide for structuring programs

(potentially) better performance

there are many popular dynamically-typed languages in industry

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/

so what do we do?

can we add a type-system?

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

history

an incomplete and likely wrong history

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

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

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

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

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

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

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

2006 Erlang's Dialyzer becomes viable Lindahl, Sagonas,

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

2006 Gradual typing for functional languages Siek, Taha,

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

2008 inspiration for typed Clojure Tobin-Hochstadt, Felleisen,

2008 introduces Occurrence typing Tobin-Hochstadt, Felleisen,

(: 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)))

state of the art

Dialyzer for Erlang

Typed Racket

Typed Clojure

Dart

Dialyzer at Basho

we write a distributed database in Erlang: Riak

correctness and fault-tolerance are import

bugs are inevitable

sometimes embarrassing

avoid preventable bugs

we use Dialyzer for this

recently hooked it up with CI

takeaways

tl;dr

several modern functional languages have optional type systems

they are mature enough to be useful

they find real bugs

and improve documentation

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

Questions? @reiddraper