attr
special-form/function
(attr obj attr-name)
Returns the value of attribute or property attr-name of obj. The compiler
generates efficient code if attr-name is a compile-time constant, otherwise
the compiler uses a call to the function attr.
make-html > (attr "hello" :length)
it: 5
make-html > (let s "length")
it: s
make-html > (attr "hello" s)
it: 5