On the pLR parsability of visual languages

The widespread use of visual languages has motivated the need for grammar-based tools to support designers in the definition and implementation of graphical environments. The effective use of such systems requires efficient parsing techniques. The VLCC system makes use of a suitable LR-like methodology that allows us to efficiently parse visual sentences. However there exist particular grammars which are non pLR parsable because they can produce run-time conflicts during the parsing of some sentences. In this paper we will introduce an algorithm that statically verifies the pLR parsability of a positional grammar by detecting whether or not it would produce run-time conflicts.