Allow binary operators to be used as lambdas (#385)

* Add operator lambdas

* Do not register anonymous functions as called functions

* Add tests

* Update CHANGELOG

* Update the docs

* Do not allow (..) to be used as a lambda

* Rename the function sum to any

test/aeso_compiler_tests.erl

@@ -795,6 +795,14 @@ failing_contracts() ->
                   [<<?Pos(2,5)
                      "Empty record definitions are not allowed. Cannot define the record `r`">>
                   ])
+    , ?TYPE_ERROR(operator_lambdas,
+                  [<<?Pos(9,32)
+                     "Cannot unify `(int, int) => int` and `(int) => 'a`\n"
+                     "when checking the application of\n"
+                     "  `(l : _, r : _) => l + r : (int, int) => int`\n"
+                     "to arguments\n"
+                     "  `1 : int`">>
+                  ])
     , ?TYPE_ERROR(warnings,
                   [<<?Pos(0, 0)
                       "The file `Triple.aes` is included but not used.">>,

test/contracts/operator_lambdas.aes

@@ -0,0 +1,14 @@
+include "List.aes"
+
+contract C =
+    type state = int
+
+    function any(l : list(bool)) : bool = List.foldl((||), false, l)
+
+    entrypoint init() =
+        let bad_application = (+)(1)
+        let good_application = (-)(3, 4)
+        let op_var = (+)
+        let op_var_application = op_var(3, 4)
+
+        good_application + op_var_application