I can't find it by searching, what is define* in guile? You can find it for instance in this answer https://stackoverflow.com/a/24101699/387194
You will find it in the documentation here: Creating advanced argument handling procedures.
6.10.4.1 lambda* and define*.
lambda* is like lambda, except with some extensions to allow optional and keyword arguments.
library syntax: lambda* ([var…]
[#:optional vardef…]
[#:key vardef… [#:allow-other-keys]]
[#:rest var | . var])
body1 body2 …
Optional and keyword arguments can also have default values to take when not present in a call, by giving a two-element list of variable name and expression. For example in
(define* (frob foo #:optional (bar 42) #:key (baz 73))
(list foo bar baz))
foo is a fixed argument, bar is an optional argument with default value 42, and baz is a keyword argument with default value 73. Default value expressions are not evaluated unless they are needed, and until the procedure is called.
Normally it’s an error if a call has keywords other than those specified by #:key, but adding #:allow-other-keys to the definition (after the keyword argument declarations) will ignore unknown keywords.
From: