private static void LoopPart(SlimChainParser cp, out Element cond, out Element use, out Element by)
{
Element c = null;
Element u = null;
Element b = null;
cp.Text("loop").Lt()
.Opt.Transfer(e => c = e, Expression)
.If(icp => icp.Text("use").Lt())
.Then(icp => icp.Transfer(e => u = e, DefaultValueVariantDeclaration))
.If(icp => icp.Text("by").Lt())
.Then(icp => icp.Transfer(e => b = e, Expression));
cond = c;
use = u;
by = b;
}
