A grammar for projectional editor

Describing a language editor can be repetitive, for instance when you have to define expressions. expression '+' expression and expression '*' expression is a typical example. From the grammar file that describes the language structure it's possible to recognize repetitive rule structures and build an editor in a consistent way.

The PE project defines a grammar and generates AST in a way not related to any projectional editor. PE4MPS project imports the generated ASTs into MPS generating for example from this rule:

Graph:
  strict=STRICT? type=GraphType name=string?
  statementList<indentList('{', '}')>=Statement*
;

this MPS editor:

The defined list of indented statement can be utilized also in:

Subgraph:
  (SUBGRAPH label=Id?)?
  statementList<indentList('{', '}')>=Statement*
;

giving:

The last example for this small introduction are optional group of elements like:

NodeId:
  id=Id (':' first=Id (':' second=Id)?)?
;

translated in MPS into two intentions:

The two mentioned project are still at their very first version and many features are still missing, probably the most important one is scopes handling.