Is there any document available with the Chuck langage syntax (conditions, loops, etc.), reserved words, meanings of => in differents contexts,
You are right on in that we don't have (and desperately need) a formal language specification that makes all of these things clear. It is a very high priority to us. We are planning to massively document (in full Java VM Spec-ish style) the syntax/semantics once objects are done.
because sometimes I see things in papers or exemples which are not described in the actual documentation.
Yes, much is missing. Our apologies. A tool (especially a language) is no good without good documentation.
Another great thing would be, describing the libraries, to indicate with the range of parameters to what they correspond (frequency, cents, midi amplitude, dB amplitude, mV amplitude, or whatever else).
Good ideas. As phil mentioned, we will do a huge update to documentation in the coming 2 months. The online docs really don't contain any of this stuff right now. We will change that. Best, Ge!