The implementation of visual programming languages (VPLs) and their supporting environments is time--consuming and tedious. To ease the implementation, researchers have developed some high level tools, which can greatly reduce the effort of developing VPLs. None of them, however, can be easily used to create a complete visual language in a seamless way like the lex/yacc tools for textual language constructions. This paper presents VisPro, a toolset for developing diagrammatic VPLs in a way similar to the lex/yacc. VisPro consists of a set of visual programming tools. It divides the process of a VPL construction into two steps: lexicon definition and grammar specification. The lexicon definition defines visual objects and a visual editor, and the language grammar is specified with graph rewriting rules (associated with actions written in Java). The compiler for the VPL is automatically created according to the grammar specification. A target VPL is a visual programming environment which..