Package: rightarrow
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            |___/https://github.com/kennknowles/python-rightarrowThis library provides a language for concise higher-order annotations
for Python programs, inspired by the syntax for higher-order contracts
and types in advanced languages. Functionality akin to contract
checking, type checking, and type inference is a work-in-progress.This project has a “duck-typed” status: Whatever you can use it for, it
is ready for :-)Here is a more concrete list of implemented and intended features:yes- Definition of a the language.yes- Parsing and printing.yes- Run-time monitoring of adherence for monomorphic annotations.upcoming- Monitoring of adherence for polymorphic annotations.upcoming- Generation of constraints between annotations in a
program.upcoming- Best-effort inference of suitable annotations.upcoming- More precise annotations to support full higher-order
design-by-contract.The AnnotationsThis language is built from the following concepts:Named types:int,long,float,complex,str,unicode,file,YourClassNameHere, …Lists:[int],[[long]], …Tuples:(int, long),(float, (int, Regex)), …Dictionaries:{string: float},{ (str, str) : [complex] }, …Unions:int|long|float,str|file, …“Anything goes”:??Functions, after which this library is named :-)str->int(int)->int(int, int)->int( (int, int) )->int( str|file )->SomeClass(int, *[str])->[(str, int)](int, *[int],**{int:str})->strObjects:object(self_type, field1: int, field2: str,...)Polymorphic types (where~a,~b,~crange over any other
type. Syntax subject to change; no preference really)~a->~a[~a]->[~a]( (~a, ~b) )->~aRun-time checkingThe moduletypelanguage.enforcecontains functions for using these
annotations as run-time monitors.Applied directly:>>> check('{string: int}', {"hello" : "there"})Wrapping a function to protect it from funky input is more interesting.
For example, putting better error checking on Python’sunicode/strinteractions (at least in Python 2)>>> '\xa3'.encode('utf-8')
...
UnicodeDecodeError: 'ascii' codec can't decode byte 0xa3 in position 0: ordinal not in range(128)

>>> @guard('unicode -> str')
... def safe_encode(s):
...    return s.encode('utf-8')

>>> safe_encode(u'hello')
'hello'
>>> safe_encode('\xa3')
TypeError: Type check failed: ? does not have type unicodeIf you are familiar with notions of “blame” for higher-order contracts,
pull-requests welcome :-)Inferring AnnotationsInference is a work-in-progress, definitely planned, and almost
certainly will always be “best effort” only. It works like so:By traversing the code, we can discover a bunch of constraints
between different missing annotations.Some of these constraints are going to be very easy to solve, so we
can just propagate the results.Some of these constraints are not going to be practical to try to
solve, so we can just drop them or insert some enforcement code if we
like.More to exploreThere are many other projects that check contracts or types for Python
in some way. They are all different, many are prototypes or research
projects, and none seem to serve the need that motivates this library.
Still, check them out!PEP 316(deferred)RPythonandPyPy(compilation-oriented)pySonarandmini-pysonar(way
cool)Pyntchtypecheckerpycontractpython-dbcandone
pyDBCandanother
pydbcandyet another
pyDBCpython-type-inference(no code, but has a great list of papers and even more tools)And there are cool things happening in other dynamic languages!Contracts in
RacketandTyped RacketTypescriptakaa slightly
gradually-typed
JavascriptandJavascript++(sort of
gradually-typed Javascript) andjavascript-contractsandcernyEste(statically-typed
coffeescript) andUberscript(gradually-typed coffeescript) andcontracts.coffeeContracts.rubyAnd this library draw inspiration from such a huge amount of academic
work it cannot possibly all be mentioned, but special thanks to these
research effortsHigher-order contracts (too numerous to mention them all!):Contracts for higher-order
functionsby Robert Bruce Findler & Matthias Felleisen.Relationally-parametric polymorphic
contractsby Arjun Guha, Jacob Matthews, Robert Bruce Findler, and Shriram
Krishnamurthi. DLS 2007.Gradual typing:Gradual typing for functional
languagesby Jeremy Siek & Walid Taha. 2006Gradual Typing for
Objectsby Jeremy
Siek and Walid Taha. ECOOP 2007.Gradual typing with unification based
inferenceby
Jeremy Siek and Manish Vachharajani. DLS 2008.Blame for
allby Amal Ahmed, Robert Bruce Findler, Jacob Matthews, and Philip
Wadler. STOP 2009.The ins and outs of of gradual type
inferenceby Aseem
Rastogi, Avik Chaudhuri, and Basil Hosmer. POPL 2012.Always available static and dynamic
feedbackby Michael Bayne, Richard Cook, and Michael D. Ernst. ICSE 2011.Hybrid Type Checking (full disclosure; I did some of this work):Hybrid type
checkingby Kenneth Knowles & Cormac Flanagan 2006/2010;Type reconstruction for general refinement
typesby
Kenneth Knowles & Cormac Flanagan, 2007.ContributorsKenn Knowles(@kennknowles)Copyright and LicenseCopyright 2012- Kenneth KnowlesLicensed under the Apache License, Version 2.0 (the “License”); you may
not use this file except in compliance with the License. You may obtain
a copy of the License athttp://www.apache.org/licenses/LICENSE-2.0Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an “AS IS” BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.