Advanced command parser and builder

[TheElectronWill]

Draft

Format

command param1 -flag --explicit value --multiple v1 v2 v3

Parameters types

• flags: boolean value present/absent
• named arguments: arbitrary value, ex. param1
• explicit arguments: --name value with one or two dashes
• multivalued arguments: --multi v1 v2 v3 ..., each value is separated by a space

Quotes

Values can be quoted to include spaces.

"single value"
'another value'
"you can use single 'quotes' in double-quoted strings and vice-versa"

Subsitution

Use $var or ${expr} or $(expr) in your command and it will be replaced by the corresponding value.

Escapements

• \n: newline
• \t: tab
• \* where * is any other character: this character as-is, not interpreted by the parser

Example

warp [set|del] home [x,y,z[,world]] [--public]

Command definition

createCommand("warp", new ManagedCommand {
  optArg("instruction")
  arg("name")
  optArg("location", LocationParser)
  optFlag("public")
  
  def execute(by: Actor, args: ArgsMap, unnamed: Seq[String]) = {
    val name = args("name") // String
    val location = args.get("location") // Option[Location]
    val isPublic = args("public") // Boolean
    val warp = findWarp(by, name)

    args("instruction") match { // Option[String]
      case None => by ! Teleport(warp.location)
      case Some("set") => ...
      case Some("del") => ...
    }
})

Implementation notes

To handle an optional optArg preceding a required arg, the parser should count the number of parameters and fill the optional arguments, in the definition order, only if there are more arguments than required.

[TheElectronWill]

Since commands are triggered asynchronously, great care should be taken about how they gather information about the command sender (and its environment). Permissions are a special case of this problem.

I offer the following solution:

1. Command declare the permissions they require and the sender's attributes they want to know about.
2. When a command is excuted, it is given the declared permissions values and attributes.

With this mechanism, command would not need to ask for external data.