Some compatibility with standard scheme idioms will be helpful in porting. about muse HOT 4 OPEN

The (define (f a b) ..) form is supported since v234 of trunk.

Call a lambda a lambda! muSE uses the symbol "fn" to mean what is referred to as
"lambda" in standard Scheme. This is 'cos muSE is used by people who might be 
scared
away if they see too many "lambda" expressions floating around ... but they
understand functions (thanks to JavaScript) and can easily read "fn" as an
abbreviation of "function". 

That said, only allowing "fn" breaks code compatibility. So now, with this 
change,
both "fn" and "lambda" can be used.

(Addition made in version 263)

A bit more about comment 2 - the standard define form.

As previously stated, muSE now supports the usual Scheme define construct for
function definition. So you can do -
  (define (f a b) body...) instead of (define f (fn (a b) body...))
  (define ((f a) b) ...) instead of (define f (fn (a) (fn (b) body...)))
etc.

Such normal constructs come with full pattern matching bind support, so that 
you can
deconstruct lists, match against constants, place guards, etc. The pattern 
matching
part of the function specification using define does not fit within the scope 
of what
is expected of Scheme.