I\'ve played around with a few functional programming languages and really enjoy the s-expr syntax used by Lisps (Scheme in particular).
I also see the advantages of
30 years ago there was lispkit lisp
Not sure how accesible it is today.
[Thats one of the places where I learnt functional programming]
There are a couple of projects that aim to use haskell underneath a lispy syntax. The older, deader, and more ponderous one is "Liskell". The newer, more alive, and lighter weight one is hasp. I think you might find it worth a look.
inconsistent and non-extendable syntax
What is "inconsistency" here?
It is odd to base a language choice soley on syntax. After all, learning syntax will take a few hours -- it is a tiny fraction of the investment required.
In comparison, important considerations like speed, typing discipline, portability, breadth of libraries, documentation and community, have far greater impact on whether you can be productive.
Ignoring all the flame bait, a quick google for immutable Scheme yields some results: http://blog.plt-scheme.org/2007/11/getting-rid-of-set-car-and-set-cdr.html