Visual programming languages (VPL) attempt to reproduce the low level constructs of general purpose programming languages and thus the complexity of the diagram becomes such that it is hard to discern the logic.
In highly domain specific areas VPLs are actually widely used. Blender 3D modelling tool is basically a graphical way of editing and visualising the underlying data structures. Now if you replace abstract syntax graph you can see the similarity.
wrt @RNeff's comment, AutoDesk Revit is a great example of how it might be possible to create a more general purpose programming language. What sets Revit apart from Verilog & VHDL is that it presents the user with context specific editors by which to set the parameters for the many different components of the designed building.
In highly domain specific areas VPLs are actually widely used. Blender 3D modelling tool is basically a graphical way of editing and visualising the underlying data structures. Now if you replace abstract syntax graph you can see the similarity.
wrt @RNeff's comment, AutoDesk Revit is a great example of how it might be possible to create a more general purpose programming language. What sets Revit apart from Verilog & VHDL is that it presents the user with context specific editors by which to set the parameters for the many different components of the designed building.