114 lines
3.4 KiB
Markdown
114 lines
3.4 KiB
Markdown
---
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title: Pursuit of a DSL
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date: 2014-08-16
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---
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A project we have been working on is [Tetra](http://github.com/Xe/Tetra). It is
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an extended services package in Go with Lua and Moonscript extensions. While
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writing Tetra, I have found out how to create a Domain Specific Language, and
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I would like to recommend Moonscript as a toolkit for creating DSL's.
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[Moonscript](http://moonscript.org) is a high level wrapper around Lua designed
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to make programming easier. We have used Moonscript heavily in Tetra because of
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how easy it is to make very idiomatic code in it.
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Here is some example code from the Tetra codebase for making a command:
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```moonscript
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require "lib/elfs"
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Command "NAMEGEN", ->
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"> #{elfs.GenName!\upper!}"
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```
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That's it. That creates a command named `NAMEGEN` that uses `lib/elfs` to
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generate goofy heroku-like application names based on names from [Pokemon Vietnamese Crystal](http://tvtropes.org/pmwiki/pmwiki.php/JustForFun/PokemonVietnameseCrystal).
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In fact, because this is so simple and elegant, you can document code like this
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inline.
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## Command Tutorial
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In this file we describe an example command `TEST`. `TEST` will return some
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information about the place the command is used as well as explain the
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arguments involved.
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Because Tetra is a polyglot of Lua, Moonscript and Go, the relevant Go objects
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will have their type definitions linked to on [godoc](http://godoc.org)
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Declaring commands is done with the `Command` macro. It takes in two arguments.
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1. The command verb
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2. The command function
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It also can take in 3 arguments if the command needs to be restricted to IRCops
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only.
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1. The command verb
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2. `true`
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3. The command function
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The command function can have up to 3 arguments set when it is called. These
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are:
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1. The [Client](https://godoc.org/github.com/Xe/Tetra/bot#Client) that
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originated the command call.
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2. The [Destination](https://godoc.org/github.com/Xe/Tetra/bot#Targeter) or
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where the command was sent to. This will be a Client if the target is an
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internal client or
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a [Channel](https://godoc.org/github.com/Xe/Tetra/bot#Channel) if the target
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is a channel.
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3. The command arguments as a string array.
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```moonscript
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Command "TEST", (source, destination, args) ->
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```
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All scripts have `client` pointing to the pseudoclient that the script is
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spawned in. If the script name is `chatbot/8ball`, the value of `client` will
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point to the `chatbot` pseudoclient.
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```moonscript
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client.Notice source, "Hello there!"
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```
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This will send a `NOTICE` to the source of the command saying "Hello there!".
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```moonscript
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client.Notice source, "You are #{source.Nick} sending this to #{destination.Target!} with #{#args} arguments"
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```
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All command must return a string with a message to the user. This is a good
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place to do things like summarize the output of the command or if it worked or
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not. If the command is oper-only, this will be the message logged to the
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services snoop channel.
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```moonscript
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"End of TEST output"
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```
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See? That easy.
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```moonscript
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Command "TEST", ->
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"Hello!"
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```
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This is much better than Cod's
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```python
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#All modules have a name and description
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NAME="Test module"
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DESC="Small example to help you get started"
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def initModule(cod):
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cod.addBotCommand("TEST", testbotCommand)
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def destroyModule(cod):
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cod.delBotCommand("TEST")
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def testbotCommand(cod, line, splitline, source, destination):
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"A simple test command"
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return "Hello!"
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```
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