from macropy.quick_lambda import macros, interned

# count how many times expensive_func runs
count = [0]
def expensive_func():
    count[0] += 1

def func():
    return interned[expensive_func()]

print(count[0] # 0)
print(count[0] # 1)
print(count[0] # 1)

The interned macro is similar to the Lazy macro in that the code within the interned[...] block is wrapped in a thunk and evaluated at most once. Unlike the lazy macro, however, interned does not created a memoizing thunk that you can pass around your program; instead, the memoization is done on a per-use-site basis.

As you can see in the example above, although func is called repeatedly, the expensive_func() call within the interned block is only ever evaluated once. This is handy in that it gives you a mechanism for memoizing a particular computation without worrying about finding a place to store the memoized values. It’s just memoized globally (often what you want) while being scoped locally, which avoids polluting the global namespace with names only relevant to a single function (also often what you want).