Lambdas ​

The type of functions in SmartPy is sp.lambda_(t1, t2, with_storage= "read-write"|"read-only"|"no-access", with_operations=True|False, with_exceptions=True|False, with_mutez_overflow=True|False, with_mutez_underflow=True|False) where t1 is the argument type and t2 the result type. It corresponds to the lambda type in Michelson.

Lambdas can be defined either using Python's lambda x: ... syntax or, when they have a name, using def f(x): ....

For example, the definition

f = lambda x: x + 1

is equivalent to:

def f(x):
    return x + 1

Here f has type sp.lambda_[sp.int, sp.int].

To call a lambda, pass it its argument in parentheses. This example calls the lambda in the previous example:

assert f(1) == 2

Effects ​

You can control the effects a lambda can have on a contract's storage by adding the @sp.effects(...) decorator to a function definition.