Local strategy definitions can be lifted to the top-level if they do not contain free variables. For example,
<verbatim>
  foo(s) = 
	 Bar(s, id)
	 ; let f = !"foobar"
		 in foobar(f)
		end
</verbatim>
can be transformed to
<verbatim>
  f = !"foobar"
  foo(s) = 
	 Bar(s, id)
	 ; foobar(f)
</verbatim>
This transformation reduces the number of nested functions in the generated C code. 
The optimization is part of the [[Stratego optimizer]] included in StrategoRelease093.

-----+++ Extension

The transformation can be extended by applying 'lambda lifting', i.e., also lift
definitions with free variables. For example,
<verbatim>
  foo(s) = 
	 Bar(s, ?x)
	 ; let f = ?"foobar"; !x
		 in foobar(f)
		end
</verbatim>
can be tranformed to
<verbatim>
  f(|x) = ?"foobar"; !x
  foo(s) = 
	 Bar(s, ?x)
	 ; foobar(f(|x))
</verbatim>
in which =x= is passed 'by value' to =f=, which has been extended with an extra
argument.

This abstraction does not work for 'by reference' variables as in the following
example:
<verbatim>
  foo(s) = 
	 ?Bar(x, y)
	 ; let f = ?FooBar(x, z)
		 in <oncetd(f)> y
		end
	 ; z
</verbatim>

-- Main.EelcoVisser - 18 Aug 2003