Polymorphic function type and lambda expression

**Problem**
Poly function types and poly function values aren't supported.

**Solution**
This implements it.

Author: eed3si9n

grammar.js

@@ -91,6 +91,8 @@ module.exports = grammar({
     [$.class_parameters],
     // 'for'  operator_identifier  ':'  _annotated_type  •  ':'  …
     [$._type, $.compound_type],
+    // 'given'  '('  '['  _type_parameter  •  ','  …
+    [$._variant_type_parameter, $.type_lambda],
     // 'if'  parenthesized_expression  •  '{'  …
     [$._if_condition, $._simple_expression],
     // _postfix_expression_choice  ':'  '('  wildcard  •  ':'  …
@@ -939,7 +941,10 @@ module.exports = grammar({
 
     function_type: $ =>
       prec.left(
-        seq(field("parameter_types", $.parameter_types), $._arrow_then_type),
+        choice(
+          seq(field("type_parameters", $.type_parameters), $._arrow_then_type),
+          seq(field("parameter_types", $.parameter_types), $._arrow_then_type),
+        )
       ),
 
     _arrow_then_type: $ =>
@@ -1104,6 +1109,15 @@ module.exports = grammar({
     lambda_expression: $ =>
       prec.right(
         seq(
+          optional(
+            seq(
+              field(
+                "type_parameters",
+                $.type_parameters,
+              ),
+              "=>",
+            ),
+          ),
           field(
             "parameters",
             choice(

test/corpus/expressions.txt

@@ -1116,7 +1116,6 @@ object O {
   { b =>
    if (c) d.e }
   { a => implicit b => b }
-  { (a: Int) ?=> (b: Int) => b }
   { (_, a) => a }
 }
 
@@ -1198,6 +1197,31 @@ object O {
             (identifier)
             (identifier))))
       (block
+        (lambda_expression
+          (bindings
+            (binding
+              (wildcard))
+            (binding
+              (identifier)))
+          (identifier))))))
+
+================================================================================
+Lambda Expression (Scala 3 syntax)
+================================================================================
+
+object O:
+  val f = (a: Int) ?=> (b: Int) => b
+
+  val less: Comparer = [X: Ord] => (x: X, y: X) => ???
+
+--------------------------------------------------------------------------------
+
+(compilation_unit
+  (object_definition
+    (identifier)
+    (template_body
+      (val_definition
+        (identifier)
         (lambda_expression
           (bindings
             (binding
@@ -1209,14 +1233,22 @@ object O {
                 (identifier)
                 (type_identifier)))
             (identifier))))
-      (block
+      (val_definition
+        (identifier)
+        (type_identifier)
         (lambda_expression
+          (type_parameters
+            (identifier)
+            (context_bound
+              (type_identifier)))
           (bindings
             (binding
-              (wildcard))
+              (identifier)
+              (type_identifier))
             (binding
-              (identifier)))
-          (identifier))))))
+              (identifier)
+              (type_identifier)))
+          (operator_identifier))))))
 
 ================================================================================
 Unit expressions

test/corpus/types.txt

@@ -140,6 +140,32 @@ object Main {
             (type_identifier)
             (type_identifier)))))))
 
+================================================================================
+Polymorphic function types (Scala 3 syntax)
+================================================================================
+
+class A:
+  type Comparer = [X: Ord] => (X, X) => Boolean
+
+--------------------------------------------------------------------------------
+
+(compilation_unit
+  (class_definition
+    (identifier)
+    (template_body
+      (type_definition
+        (type_identifier)
+        (function_type
+          (type_parameters
+            (identifier)
+            (context_bound
+              (type_identifier)))
+          (function_type
+            (parameter_types
+              (type_identifier)
+              (type_identifier))
+            (type_identifier)))))))
+
 ================================================================================
 Context function types (Scala 3 syntax)
 ================================================================================