Kawa implements all the required and optional features of R7RS, with the following exceptions.
The entire "numeric tower" is implemented. However, some transcendental function only work on reals. Integral function do not necessarily work on inexact (floating-point) integers. (The whole idea of "inexact integer" in R5RS seems rather pointless ...)
call-with-current-continuation is only "upwards" (?).
I.e. once a continuation has been exited, it cannot be invoked.
These restricted continuations can be used to implement catch/throw
(such as the examples in R4RS), but not co-routines or backtracking.
Kawa now does general tail-call elimination, but only if
you use the flag
--full-tail-calls. (Currently, the
eval function itself is not fully tail-recursive, in violation
of R5RS.) The
--full-tail-calls flag is not on by default,
partly because it is noticably slower (though I have not measured how
much), and partly I think it is more useful for Kawa to be compilatible
with standard Java calling conventions and tools.
Code compiled with
--full-tail-calls can call code
compiled without it and vice versa.
--full-tail-calls, if the
compiler can prove that the procedure being called is the current
function, then the tail call will be replaced by a jump.
This includes must “obvious” cases of calls to the
current function named using
and many cases of mutual tail-recursion (including
equal? predicate does not handle infinite (self-referential)
data structures. (Checking for cycles is difficult to implement efficiently.)
By default, symbols are case sensitive.
Kawa implements most of the features of the expression language of DSSSL,
the Scheme-derived ISO-standard Document Style Semantics and Specification
Language for SGML. Of the core expression language, the only features
missing are character properties,
the time-relationed procedures, and character name escapes in
From the full expression language, Kawa additionally is missing
format-number-list, and language objects.
Quantities, keyword values, and the expanded
(with optional and keyword parameters) are supported.