Defines a function.
In its define flavour, will take a function body and assign it to
variable.
define sum a, b # make variable 'sum' hold the function
+
a
b
# yields the function, like `fun` and `def` do
sum 1 2
# will yield 3
In the fun and def flavours, the function is unnamed, it's thus not
bound in a local variable.
map [ 1, 2, 3 ]
def x
+ x 3
# yields [ 4, 5, 6 ]
It's OK to generate the function name at the last moment:
sequence
set prefix "my"
define "$(prefix)-sum" a b
+ a b