nitcc: add groupize to create anonymous productions

Signed-off-by: Jean Privat <[email protected]>

contrib/nitcc/src/nitcc.sablecc

@@ -111,6 +111,7 @@ elem =
 	{star:} elem '*' |
 	{ques:} elem '?' |
 	{plus:} elem '+' |
+	{group:} '(' elem+ ')' |
 	{empty:} 'Empty' ;
 
 priority =

contrib/nitcc/src/nitcc_semantic.nit

@@ -157,6 +157,22 @@ private class CheckNameVisitor
 		return prod
 	end
 
+	# Pool for anoymous grouped production (reuse them!)
+	var groupizes = new HashMap[Array[Element], Production]
+
+	# Create an anonymous production that groups some elements.
+	# Note: an anonymous production is always returned, even if `es` is empty or single.
+	fun groupize(es: Array[Element]): Production
+	do
+		if groupizes.has_key(es) then return groupizes[es]
+		var name = "_group{groupizes.length}"
+		var prod = new Production(name)
+		v1.gram.prods.add(prod)
+		var a1 = prod.new_alt2("{name}_single", es)
+		groupizes[es] = prod
+		return prod
+	end
+
 	# The current nexpr, used to track dependency on named expressions (see `Nexpr::precs`)
 	var nexpr: nullable Nexpr = null
 
@@ -703,6 +719,17 @@ redef class Nelem_plus
 	end
 end
 
+redef class Nelem_group
+	redef fun accept_check_name_visitor(v) do
+		var old = v.elems
+		v.elems = new Array[Element]
+		super
+		var elem = v.groupize(v.elems)
+		v.elems = old
+		set_elem(v, null, elem)
+	end
+end
+
 redef class Ntree_part
 	redef fun accept_collect_prod(v) do
 		print "NOT YET IMPLEMENTED: `Tree` part; it is ignored"