Functions in Opshin should have type annotations for the arguments and the return.
There must be one
return statement at the end of a function.
If it is omitted, the function returns
Note that the
returnstatement must be the last statement in a function, if present
def fibonacci(n: int) -> int: if n < 2: res = 1 else: res = fibonacci(n-1) + fibonacci(n-2) return res
As shown, Opshin functions support recursion.
Generally OpShin discourages the use of lambda functions, as they don't allow specifying types in the function signature. Instead, consider using a local function definitions or list expressions. For example instead of the following expression
ys = map(lambda x: 2*x, filter(lambda x: x > 0, xs))
You could either define local functions like this
def greater_zero(x: int) -> bool: return x > 0 def mul_2(x: int) -> int: return 2*x ys = map(mul_2, filter(greater_zero, xs))
Or you can express this very compactly and readable directly in a list expression like this
ys = [2*x for x in xs if x > 0]
Note that you can define functions locally and within other functions, so that they do not clutter your namespace and can not be used in the wrong context. The following is legal.
def mul_twice(x: int) -> int: def mul_once(x: int) -> int: return x * x return mul_once(x) * mul_once(x)