Today, I added a keyword called "freeze" to Marvin3. Basically, when called inside a routine, it pops the top element from the stack and replaces routine's code with a word that pushes that value onto the stack; this way we can create a "write-once" routine, which is similar to C#'s readonly modifier (value is allowed to be set once). Consider the following example:
:YOUR-NUMBER input int freeze ;
"Enter a number:" prints YOUR-NUMBER
YOUR-NUMBER " is a nice number!" cat println
Notice that, although YOUR-NUMBER is a routine, when called it just pushes the same value determined when it is first called.
Here is a more complex one; the following set of class and routines implement a generator that returns subsequent numbers starting from 1 (then 2, 3, ...)
@__generate 0 !n [%n incr ^n] dup ;
:_generate __generate freeze ;
:generate _generate call ;
The Python equivalent is (although using generators would be better):
class _generate:
def __init__(self):
self.n = 0
def __call__(self):
self.n += 1
return self.n
generate = _generate()
