ychr-0.1.0.0: examples/closures.chr

% Anonymous lambdas, function references, and closures.
%
% `double/1` is an ordinary function. `make_adder/1` returns a
% *closure*: a lambda that captures the argument N from its enclosing
% scope. Both are invoked via the prelude's `call/2`, which applies
% any callable value to its argument.
%
% Three constraints each demonstrate one form of callable:
%   - by_ref(R):  pass an existing function by reference.
%   - lambda(R):  pass an anonymous lambda.
%   - closure(R): build a closure with make_adder, then call it.
%
% Used by docs/tutorials/04-functions-and-types.md §3.

:- module(callables,
          [by_ref/1, lambda/1, closure/1,
           fun double/1, fun make_adder/1]).
:- chr_constraint by_ref/1, lambda/1, closure/1.
:- function double/1.
:- function make_adder/1.

double(X) -> X + X.

make_adder(N) -> fun(X) -> X + N end.

by_ref(R)  <=> R is call(fun double/1, 21).
lambda(R)  <=> R is call(fun(X) -> X * X end, 7).
closure(R) <=> Add10 is make_adder(10), R is call(Add10, 5).