Lambdas
Lambda expressions in Fuzion are syntactic sugar to produce values of function types.
Depending on the number of arguments, lambdas will create anonymous features
that inherit from the Fuzion standard library features Function
(general functions), Unary (functions with one argument, they
can be composed), or Lazy (functions with no argument). Unary and
lazy functions can be assigned to variables of type Function as well,
if so desired.
Examples of Lambdas
A lambda expression is of the form a,b -> f a b or (a,b)
-> f a b where a and b are the arguments of the
lambda expression and f a b is an arbitrary expressions using these
arguments to calculate a results. The following example uses a lambda
expression x -> "Hello $x!" to map a sequence of names
to strings that greet these persons. Then, a second lambda x -> say
x is called for_each of these greetings to be printed:
In the next example, we use two lambda expressions to determine the average
age from a sequence of persons given as tuples of their names and ages.
First p -> p.1 is used to select the second part of the tuple, the
age and calculate the sum of all ages. Next, p -> 1 is used to
count the number of persons by summing up a 1 for each person:
Placeholder _
In the previous example, the lambda p -> 1 introduced a
parameter p that was not needed in the subsequent
expression. Whenever this is the case, an underscore _ can be used
as a placeholder for an ignored parameter: _ -> 1:
Empty argument list
Lambdas might be nullary functions, i.e., there might be no arguments at
all. In this case, the empty argument list must be enclosed by
parentheses () as in the following code. Here, a
feature repeat performs an action repeatedly until that action
returns false.
The Fuzion syntax permits the expression following -> to be
a block extending several lines at a higher indentation level. This is used in
this example to count the number of calls in a mutable variable, print that
count and to return false as soon as 10 iterations have been
reached.