I am currently developing a programming language. Its strongly

Haskell's missing liquid types. Be sure to implement that.

>>57490809
I am programming Haskell for quite a long time ... But I have actualy no idea what liquid types are... Maybe i know them by another name... Could you give me a source?

not syntactic sugar but rather the opposite. All languages have syntactic sugar. But make a layer of homoiconicity. Define an AST object that is easy to deal with so it can be modified through a preprocessor scheme, so to allow for new constructs in the language.
In Scheme, "hygienic" macros are just rearrangements of the symbols. In CL macros are far more powerful, having the full lisp runtime available at macro processing. A middleground would be okay, having a specific set of actions that could be carried (in the manner of how C does stuff according to #ifdef's perhaps?).
I see that you're mostly getting your inspiration from MLs, so you could keep the domain of such macros withing the MLs without getting a lisp.
On the other hand you could allow the user to define his or her own syntactic sugar through a combination of a preprocessed regexp and macro capabilities.

>>57490767
I miss the Common Lisp condition system. I miss design by contract.

>>57490767
Row polymorphism. A modern object-oriented language shouldn't come without it.

https://www.cl.cam.ac.uk/teaching/1415/L28/rows.pdf