muScript: support complex bind expressions

muscript/src/main/java/io/gitlab/jfronny/muscript/compiler/Parser.java

@@ -242,8 +242,14 @@ public class Parser {
                     yield new Get(start, end, asDynamic(expr), Expr.literal(name.start, name.current - 1, name.lexeme));
                 }
                 case DoubleColon -> {
-                    TokenData name = consume(Token.Identifier, "Expected variable name after '::'.");
-                    yield new Bind(start, end, new Variable(name.start, name.current - 1, name.lexeme), expr.asDynamicExpr());
+                    DynamicExpr callable;
+                    if (match(Token.Identifier)) {
+                        callable = new Variable(previous.start, previous.current - 1, previous.lexeme);
+                    } else if (match(Token.LeftParen)) {
+                        callable = expression().asDynamicExpr();
+                        consume(Token.RightParen, "Expected ')' after expression.");
+                    } else throw error("Bind operator requires right side to be a literal identifier or to be wrapped in parentheses.");
+                    yield new Bind(start, end, callable, expr.asDynamicExpr());
                 }
                 case LeftBracket -> {
                     expr = new Get(start, end, asDynamic(expr), expression());

muscript/src/test/java/io/gitlab/jfronny/muscript/test/BindTest.java

@@ -21,4 +21,18 @@ class BindTest {
                 numbers::map({n->n::function(2)})::filter({n->n%2!=0})
                 """).asExpr().asStringExpr().get(makeArgs()));
     }
+
+    @Test
+    void complexBind() {
+        // fn = {b -> 2 * b}
+        assertEquals(6, Parser.parseScript("""
+                fn = 2::({a, b -> a * b})
+                fn(3)
+                """).asExpr().asNumberExpr().get(makeArgs()));
+        // {a, b, c -> a(b(c))}(fn, {a -> a + 5}, 3)
+        assertEquals(16, Parser.parseScript("""
+                fn = 2::({a, b -> a * b})
+                fn::({a, b, c -> a(b(c))})({a -> a + 5}, 3)
+                """).asExpr().asNumberExpr().get(makeArgs()));
+    }
 }