The language IO has a very simple grammar[1] and ignoring libraries is a pretty productive language.

I suspect that you are on to something, but instead of the grammer being the guide instead the abstraction that the language gives you, but with a correlation between abstraction and the complexity of the grammar.

[1] http://iolanguage.org/scm/io/docs/IoGuide.html exp ::= { message | terminator } message ::= symbol [arguments] arguments ::= "(" [exp [ { "," exp } ]] ")" symbol ::= identifier | number | string terminator ::= "\n" | ";"