Speaking of composeable grammars, if you were not already aware JetBrains (maker of the wholly incredible, and now Open Source, IntelliJ) has a language platform which is targeting just that kind of thing.
Be forewarned that MPS is almost a closed system. One must develop the grammar only in MPS (no textual grammar to speak of), and the editor for the language described by that grammar is then defined using this bizarre form-layout language (also edited in MPS). One cannot (that I am aware of) take the newly created MPS system for that language and point it at your favorite source code text file. It does have a seemingly powerful code generation system, so it might be possible to generate the textual grammar if you were so inclined. However, the text generator also uses a bizarre language so that is likely more pain than one would wish to endure.
The advantage of a system such as that is that there is only The One True Brace Style(tm) because the "braces" and other punctuation are merely icons to please the eye; they are not "editable" like in Emacs.
They call it Meta Programming System (http://www.jetbrains.com/mps/) and it is also Open Source.
Be forewarned that MPS is almost a closed system. One must develop the grammar only in MPS (no textual grammar to speak of), and the editor for the language described by that grammar is then defined using this bizarre form-layout language (also edited in MPS). One cannot (that I am aware of) take the newly created MPS system for that language and point it at your favorite source code text file. It does have a seemingly powerful code generation system, so it might be possible to generate the textual grammar if you were so inclined. However, the text generator also uses a bizarre language so that is likely more pain than one would wish to endure.
The advantage of a system such as that is that there is only The One True Brace Style(tm) because the "braces" and other punctuation are merely icons to please the eye; they are not "editable" like in Emacs.