---++ Introduction

==rtg2typematch== is a tool for generating a duck-typing-based strategies that check if an ATerm is of a type as defined in an [[RegularTreeGrammar][RTG]]. An example will make this more clear.

---++ Example

Let's take the RTG produced by the example in the manual page of [[%MANUAL%/ref-sdf2rtg.html][sdf2rtg]]:
<verbatim>
  regular tree grammar
	 start Exp
	 productions
		Exp		-> Minus(Exp,Exp)
		Exp		-> Plus(Exp,Exp)
		Exp		-> Mod(Exp,Exp)
		Exp		-> Div(Exp,Exp)
		Exp		-> Mul(Exp,Exp)
		Exp		-> Int(IntConst)
		Exp		-> Var(Id)
		IntConst -> <string>
		Id		 -> <string>
</verbatim>

Apply rtg2typematch:

<verbatim>
  > rtg2typematch -i Exp.rtg -o Exp-typematch.str
</verbatim>

will result in the module
<verbatim>
  module Exp-typematch
  strategies
	 is-Exp =
		?Minus(_, _)
		+ ?Plus(_, _)
		  + ?Mod(_, _)
			 + ?Div(_, _)
				+ ?Mul(_, _)
				  + ?Int(_)
					 + ?Var(_)

	 is-IntConst =
		is-string

	 is-Id =
		is-string
</verbatim>

You can call =is-Exp= to check whether a term is of sort Exp. 
Notice that the generated code only looks at the name of the
constructor. If the same constructor can be used to produce
different sorts, the typematch strategy of all these sort will
accept a term that is an application of this constructor.