>Is it perhaps so that there exists a language that is trivial to implement, yet also super powerful and expressive to program in (don't say lisp here, though it does almost satisfy the second constraint imo).
Lisp. Satisfies both constraints.
But seriously, Forth is another interesting language that strikes a good balance between ease of implementation vs ease of use and expressive power. But even more than Lisp, it takes some serious getting used to.
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" | ";"
Interesting observation. I think, the more abstraction, the more productive you can be.
The implications seem more subtle and are more interesting. The very simple phenomenon implies that application development time later can be saved by compiler development time now. If so then what is the most optimal language/compiler? What is the best distribution of time? Is it perhaps so that there exists a language that is trivial to implement, yet also super powerful and expressive to program in (don't say lisp here, though it does almost satisfy the second constraint imo).