init

.github/workflows/main.yml

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+name: Ruby
+
+on:
+  push:
+    branches:
+      - main
+
+  pull_request:
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    name: Ruby ${{ matrix.ruby }}
+    strategy:
+      matrix:
+        ruby:
+          - '3.2.0'
+
+    steps:
+    - uses: actions/checkout@v4
+    - name: Set up Ruby
+      uses: ruby/setup-ruby@v1
+      with:
+        ruby-version: ${{ matrix.ruby }}
+        bundler-cache: true
+    - name: Run the default task
+      run: bundle exec rake

.gitignore

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+/.bundle/
+/.yardoc
+/_yardoc/
+/coverage/
+/doc/
+/pkg/
+/spec/reports/
+/tmp/

.rubocop.yml

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+AllCops:
+  TargetRubyVersion: 3.0
+
+Style/StringLiterals:
+  EnforcedStyle: double_quotes
+
+Style/StringLiteralsInInterpolation:
+  EnforcedStyle: double_quotes

CHANGELOG.md

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+## [Unreleased]
+
+## [0.1.0] - 2024-03-23
+- Initial release

Gemfile

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+# frozen_string_literal: true
+
+source "https://rubygems.org"
+
+# Specify your gem's dependencies in expressive.gemspec
+gemspec
+
+gem "rake", "~> 13.0"
+
+gem "minitest", "~> 5.16"
+
+gem "rubocop", "~> 1.21"

LICENSE.txt

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+The MIT License (MIT)
+
+Copyright (c) 2024 Omkar Moghe
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in
+all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+THE SOFTWARE.

README.md

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+# Expressive
+
+A simple and flexible Ruby library to build and evaluate mathematical or other expressions.
+
+## Installation
+
+Install the gem and add to the application's Gemfile by executing:
+
+    $ bundle add expressive
+
+If bundler is not being used to manage dependencies, install the gem by executing:
+
+    $ gem install expressive
+
+## Usage
+
+### Models
+
+#### Scalar
+
+A `Scalar` is the simplest object that can be evaluated. It holds a single `value`. When used in an `Expression`, this `value` must respond to the symbol (i.e. support the method) defined by the `Expression#operator`.
+
+```ruby
+Scalar.new(1)
+```
+
+#### Variable
+
+A `Variable` represents a named value stored in the `Environment`. Unlike `Scalars`, `Variables` have no value until they are evaluated by an `Environment`. Evaluating a `Variable` that isn't present in the `Environment` will result in a `MissingVariableError`.
+
+```ruby
+Variable.new("variable_a")
+```
+
+#### Expression
+
+An expression represents 2 or more `operands` that are reduced using a defined `operator`. The `operands` of an `Expression` can be `Scalars`, `Variables`, or other `Expressions`. All `operands` must `respond_to?` the method defined by the `operator`.
+
+And `Expression` can store its result back into the `Environment` by defining an `output`.
+
+```ruby
+# addition
+Expression.new(:+, Scalar.new(1), Scalar.new(2))
+
+# multiplication
+Expression.new(:*, Variable.new("variable_a"), Scalar.new(2))
+
+# storing output
+Expression.new(:+, Scalar.new(1), Scalar.new(2), output: "one_plus_two")
+```
+
+#### Environment
+
+The `Environment` holds state in the form of a `variables` hash and can evaluate `Expressions`, `Scalars`, and `Variables` within a context. The environment handles updates to the state as `Expressions` run.
+
+```ruby
+environment = Environment.new(
+  "variable_a" => 1,
+  "variable_b" => 2,
+)
+
+environment.evaluate(Variable.new("variable_a"))
+#=> 1
+
+environment.evaluate(
+  Expression.new(
+    :+,
+    Variable.new("variable_a"),
+    Variable.new("variable_b"),
+    output: "variable_c" # defines where to store the result value
+  )
+)
+#=> 3
+
+environment.variables
+#=> { "variable_a" => 1, "variable_b" => 2, "variable_c" => 3 }
+```
+
+When evaluating multiple objects at a time, the value of the _last_ object will be returned.
+
+```ruby
+environment = Environment.new
+environment.evaluate(
+  Scalar.new(1),
+  Expression.new(:+, Scalar.new(1), Scalar.new(2))
+)
+#=> 3
+```
+
+### Serialization (to JSON)
+
+All models support serialization via:
+- `as_json`: builds a serializable hash representation of the object
+- `to_json`: builds a JSON string representing the object
+
+### Building (from JSON)
+
+<!-- TODO -->
+
+### Beyond math
+
+<!-- TODO -->
+
+## Development
+
+After checking out the repo, run `bin/setup` to install dependencies. Then, run `rake test` to run the tests. You can also run `bin/console` for an interactive prompt that will allow you to experiment.
+
+To install this gem onto your local machine, run `bundle exec rake install`. To release a new version, update the version number in `version.rb`, and then run `bundle exec rake release`, which will create a git tag for the version, push git commits and the created tag, and push the `.gem` file to [rubygems.org](https://rubygems.org).
+
+## Contributing
+
+Bug reports and pull requests are welcome on GitHub at https://github.com/omkarmoghe/expressive.
+
+## License
+
+The gem is available as open source under the terms of the [MIT License](https://opensource.org/licenses/MIT).

Rakefile

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+# frozen_string_literal: true
+
+require "bundler/gem_tasks"
+require "minitest/test_task"
+
+Minitest::TestTask.create
+
+require "rubocop/rake_task"
+
+RuboCop::RakeTask.new
+
+task default: %i[test rubocop]

bin/console

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+#!/usr/bin/env ruby
+# frozen_string_literal: true
+
+require "bundler/setup"
+require "expressive"
+
+# You can add fixtures and/or initialization code here to make experimenting
+# with your gem easier. You can also use a different console, if you like.
+
+require "irb"
+IRB.start(__FILE__)

bin/setup

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+#!/usr/bin/env bash
+set -euo pipefail
+IFS=$'\n\t'
+set -vx
+
+bundle install
+
+# Do any other automated setup that you need to do here

expressive.gemspec

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+# frozen_string_literal: true
+
+require_relative "lib/expressive/version"
+
+Gem::Specification.new do |spec|
+  spec.name = "expressive"
+  spec.version = Expressive::VERSION
+  spec.authors = ["Omkar Moghe"]
+  spec.email = ["theomkarmoghe@gmail.com"]
+
+  spec.summary = "A simple and flexible Ruby library to build and evaluate mathematical or other expressions."
+  spec.homepage = "https://github.com/omkarmoghe/expressive"
+  spec.license = "MIT"
+  spec.required_ruby_version = ">= 3.0.0"
+
+  spec.metadata["allowed_push_host"] = "TODO: Set to your gem server 'https://example.com'"
+
+  spec.metadata["homepage_uri"] = spec.homepage
+  spec.metadata["source_code_uri"] = spec.homepage
+  spec.metadata["changelog_uri"] = "TODO: Put your gem's CHANGELOG.md URL here."
+
+  # Specify which files should be added to the gem when it is released.
+  # The `git ls-files -z` loads the files in the RubyGem that have been added into git.
+  gemspec = File.basename(__FILE__)
+  spec.files = IO.popen(%w[git ls-files -z], chdir: __dir__, err: IO::NULL) do |ls|
+    ls.readlines("\x0", chomp: true).reject do |f|
+      (f == gemspec) ||
+        f.start_with?(*%w[bin/ test/ spec/ features/ .git .github appveyor Gemfile])
+    end
+  end
+  spec.bindir = "exe"
+  spec.executables = spec.files.grep(%r{\Aexe/}) { |f| File.basename(f) }
+  spec.require_paths = ["lib"]
+
+  # Uncomment to register a new dependency of your gem
+  # spec.add_dependency "example-gem", "~> 1.0"
+
+  # For more information and examples about making a new gem, check out our
+  # guide at: https://bundler.io/guides/creating_gem.html
+end

lib/expressive.rb

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+# frozen_string_literal: true
+
+require_relative "expressive/version"
+
+module Expressive
+  class Error < StandardError; end
+  # Your code goes here...
+end

lib/expressive/version.rb

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+# frozen_string_literal: true
+
+module Expressive
+  VERSION = "0.1.0"
+end

sig/expressive.rbs

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+module Expressive
+  VERSION: String
+  # See the writing guide of rbs: https://github.com/ruby/rbs#guides
+end

test/test_expressive.rb

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+# frozen_string_literal: true
+
+require "test_helper"
+
+class TestExpressive < Minitest::Test
+  def test_that_it_has_a_version_number
+    refute_nil ::Expressive::VERSION
+  end
+
+  def test_it_does_something_useful
+    assert false
+  end
+end

test/test_helper.rb

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+# frozen_string_literal: true
+
+$LOAD_PATH.unshift File.expand_path("../lib", __dir__)
+require "expressive"
+
+require "minitest/autorun"