(1) This language has been invented long ago; its name is Haskell. Eta is a JVM backend / target for it.
(2) A good general-purpose language is good at creating pseudo-DSLs, also known as abstractions or APIs. This can include customized syntax, but usually it's not a brilliant idea. DSLs using the common syntax are quite prevalent in Lisp / Scheme / Clojure, or in Ruby. Haskell is reasonably good at creating DSLs, much better than e.g. Java.
(2) A good general-purpose language is good at creating pseudo-DSLs, also known as abstractions or APIs. This can include customized syntax, but usually it's not a brilliant idea. DSLs using the common syntax are quite prevalent in Lisp / Scheme / Clojure, or in Ruby. Haskell is reasonably good at creating DSLs, much better than e.g. Java.