# Speculation [![Build Status](https://travis-ci.org/english/speculation.svg?branch=master)](https://travis-ci.org/english/speculation)

A Ruby port of Clojure's `clojure.spec`. This library is largely a copy-and-paste from clojure.spec so all credit goes to Rich Hickey and contributors for their original work.

See [clojure.spec - Rationale and Overview](https://clojure.org/about/spec) for a thorough outline of the problems clojure.spec (and thus Speculation) was built to address and how it addresses them. As a brief summary, Speculation allows you to write predicate specs (nothing to do with RSpec!) which enable:

* declarative data validation and destructuring
* error reporting
* runtime method instrumentation, argument checking and stubbing
* generative testing

## Project Goals

The goal of this project is to match clojure.spec as closely as possible, from design to features to API. There aren't, and won't be any, significant departures from clojure.spec.

## Examples

* [sinatra-web-app](examples/sinatra-web-app): A small Sinatra web application demonstrating parameter validation and API error message generation.
* [spec_guide.rb](examples/spec_guide.rb): Speculation port of Clojure's [spec guide](https://clojure.org/guides/spec), demonstrating most features.
* [codebreaker.rb](examples/codebreaker.rb): Speculation port of the 'codebreaker' game described in [Interactive development with clojure.spec](http://blog.cognitect.com/blog/2016/10/5/interactive-development-with-clojurespec)
* [json_parser.rb](examples/json_parser.rb): JSON parser using Speculation.

## Usage

Documentation is available at [RubyDoc](http://www.rubydoc.info/github/english/speculation). The API is more-or-less the same as `clojure.spec`. If you're already familiar clojure.spec with then you should feel at home with Speculation. Most guides, talks and discussion around clojure.spec should apply equally well to Speculation. Clojure and Ruby and quite different languages, so naturally there are some differences:

## Differences with clojure.spec

### Built in predicates

clojure.spec utilises its rich standard library of predicate functions and data structures when writing specs. Ruby has neither of those, so we must be creative with what we define as a 'predicate' in Speculation. Each of the following are valid Speculation predicates:

```rb
S.valid?(->(x) { x > 0 }, 2)
S.valid?(:even?.to_proc, 2)
S.valid?(String, "foo")
S.valid?(Enumerable, [1, 2, 3])
S.valid?(/^\d+$/, "123")
S.valid?(Set[:foo, :bar, :baz], :foo)
```

### Namespaced keywords/symbols

Namespaced keywords are at the core of `clojure.spec`. Since clojure.spec utilises a global spec registry, namespaced keywords allow libraries to register specs with the same names but under different namespaces, thus removing accidental collisions. Ruby's equivalent to Clojure's keywords are Symbols. Ruby Symbol's don't have namespaces.

In order keep the global spec registry architecture in Speculation, we utilise a helper method `ns` to achieve similar behaviour:

```rb
module MyModule
  extend Speculation::NamespacedSymbols

  p ns(:foo)
  # => :"MyModule/foo"

  p ns(AnotherModule, :foo)
  # => :"AnotherModule/foo"
end
```

### FSpecs

#### Symbols/Methods

Clojure uses Symbols to refer to functions. To refer to a method in Ruby, we must use the `method` method.

```rb
def self.hello(name)
  "Hello #{name}"
end

S.fdef(method(:hello), :args => S.cat(:name => String), :ret => String)
```

#### Block args

In addition to regular arguments which can easily be described as a list, Ruby methods can take blocks. In Speculation, we spec a method's block separately to its args:

```rb
def self.hello(name, &block)
  "Hello #{block.call(name)}"
end

S.fdef(method(:hello), :args => S.cat(:name => String),
                       :block => S.fspec(:args => S.cat(:s => String), :ret => String),
                       :ret => String)
```

#### Generators and quick check

Speculation uses [`Rantly`](https://github.com/abargnesi/rantly) for random data generation. Generator functions in Speculation are Procs that take one argument (Rantly instance) and return a random value. While Clojure's test.check generators generate values that start small and continue to grow and get more complex as a property holds true, Rantly always generates random values.

Rantly gives Speculation the ability to shrink a failing test case down to its smallest failing case, however in Speculation we limit this to Integers and Strings. This is an area where Speculation may currently be significantly weaker than clojure.spec.

## Project status

Speculation will mirror any changes made to clojure.spec. clojure.spec is still in alpha so breaking changes should be expected.

While most of features of clojure.spec are implemented in Speculation, a few remain:

- [`unform`](https://clojuredocs.org/clojure.spec/unform)
- [`form`](https://clojuredocs.org/clojure.spec/form)
- [`abbrev`](https://clojuredocs.org/clojure.spec/abbrev)
- [`describe`](https://clojuredocs.org/clojure.spec/describe)

## Improvements

Some things I hope to focus on in the near future:

- Explore alternative generator library
  - Build up a library of generators around Rantly in the meantime?
- Generate documentation from specs
  - perhaps integrating with [Pry's documentation browsing](https://github.com/pry/pry/wiki/Documentation-browsing)?
- Profile and optimise

## Development

After checking out the repo, run `bin/setup` to install dependencies. Then, run `rake` to run rubocop and the tests. You can also run `bin/console` for an interactive prompt that will allow you to experiment.

## Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/english/speculation.

## License

The gem is available as open source under the terms of the [MIT License](http://opensource.org/licenses/MIT).