Lambdas are constrained by their type. If you see a lambda being passed to, let's say `map`, then (assuming you know the type of `map`) you know the type of the passed lambda.
Of course this assumes the lambda is pure, but in the kind of code we're talking about (pseudofunctional code with lots of higher-order functions) they should be pure for the most part.
Of course this assumes the lambda is pure, but in the kind of code we're talking about (pseudofunctional code with lots of higher-order functions) they should be pure for the most part.