diff --git a/corpus/test.langexp b/corpus/test.langexp
index f5ace2a..5146c0e 100644
--- a/corpus/test.langexp
+++ b/corpus/test.langexp
@@ -51,7 +51,7 @@ sum 'a 'b = 'a + 'b;
 : also this is example of function constraint
 @n is position in Fibonacci sequence
 ? 'n >= 0;
-fib @n 'n : Int -> Int =
+fib 'n : @n Int -> Int =
   'n =: 0 | 1 => 1
      =: _ => fib ('n - 1) + fib 'n;
 
@@ -149,10 +149,6 @@ bubble_sort 'arr : ref Array['A] = {
   };
 }
 
-merge_sort 'arr : <> Array['A] = {
-
-}
-
 : example of ^ and generics. ^ used to denote that this object allocated on heap
 : object allocated by unique reference by default
 ^TreeNode 'Key 'Value =
@@ -213,6 +209,18 @@ arg_deduction_example 'name 'duration : <- String <- Float -> Task = Task 'name
   $is_less_then : Ord -> Bool;
 }
 
+: function, that takes result argument
+result_example 'a! = 'a =: _? => print "value inside"
+                        =: _ => print "error inside";
+
+: function, that returns result
+parse_number : Unit! = {
+  %number_str := String.scan;
+  %number! := Int.parse number_str;
+  number.print;
+  bring ();
+}
+
 --------------------------------------------------------------------------------
 
 (source_file
@@ -315,7 +323,9 @@ arg_deduction_example 'name 'duration : <- String <- Float -> Task = Task 'name
         (return
           (unit_literal)))))
   (function_definition
-    (definition_info)
+    (definition_info
+      (info)
+      (info))
     (simple_name_identifier)
     (argument_name_identifier)
     (argument_name_identifier)
@@ -345,11 +355,14 @@ arg_deduction_example 'name 'duration : <- String <- Float -> Task = Task 'name
         (placeholder)
         (null_literal))))
   (function_definition
-    (definition_info)
+    (definition_info
+      (info))
     (annotation_info
-      (annotation_identifier))
+      (annotation_identifier)
+      (info))
     (annotation_info
-      (annotation_identifier))
+      (annotation_identifier)
+      (info))
     (simple_name_identifier)
     (argument_name_identifier)
     (argument_name_identifier)
@@ -360,9 +373,13 @@ arg_deduction_example 'name 'duration : <- String <- Float -> Task = Task 'name
       (name_expression
         (argument_name_identifier))))
   (function_definition
-    (definition_info)
+    (definition_info
+      (info)
+      (info)
+      (info))
     (annotation_info
-      (annotation_identifier))
+      (annotation_identifier)
+      (info))
     (constraint
       (operator_expression
         (name_expression
@@ -599,7 +616,8 @@ arg_deduction_example 'name 'duration : <- String <- Float -> Task = Task 'name
           (simple_name_identifier)
           (number_literal)))))
   (function_definition
-    (definition_info)
+    (definition_info
+      (info))
     (operator)
     (argument_name_identifier)
     (argument_name_identifier)
@@ -660,7 +678,8 @@ arg_deduction_example 'name 'duration : <- String <- Float -> Task = Task 'name
         (type
           (simple_type_identifier)))))
   (function_definition
-    (definition_info)
+    (definition_info
+      (info))
     (simple_name_identifier)
     (argument_name_identifier)
     (type
@@ -725,7 +744,8 @@ arg_deduction_example 'name 'duration : <- String <- Float -> Task = Task 'name
                 (operator)
                 (bool_literal))))))))
   (function_definition
-    (definition_info)
+    (definition_info
+      (info))
     (simple_name_identifier)
     (argument_name_identifier)
     (type
@@ -789,16 +809,10 @@ arg_deduction_example 'name 'duration : <- String <- Float -> Task = Task 'name
                   (simple_name_identifier))
                 (operator)
                 (bool_literal))))))))
-  (function_definition
-    (simple_name_identifier)
-    (argument_name_identifier)
-    (type
-      (simple_type_identifier)
-      (type
-        (argument_type_identifier)))
-    (block))
   (type_definition
-    (definition_info)
+    (definition_info
+      (info)
+      (info))
     (simple_type_identifier)
     (argument_type_identifier)
     (argument_type_identifier)
@@ -921,7 +935,8 @@ arg_deduction_example 'name 'duration : <- String <- Float -> Task = Task 'name
               (simple_name_identifier)
               (number_literal)))))))
   (function_definition
-    (definition_info)
+    (definition_info
+      (info))
     (simple_name_identifier)
     (argument_name_identifier)
     (argument_name_identifier)
@@ -933,7 +948,8 @@ arg_deduction_example 'name 'duration : <- String <- Float -> Task = Task 'name
         (simple_name_identifier)
         (argument_name_identifier))))
   (function_definition
-    (definition_info)
+    (definition_info
+      (info))
     (simple_name_identifier)
     (argument_name_identifier)
     (argument_name_identifier)
@@ -962,7 +978,8 @@ arg_deduction_example 'name 'duration : <- String <- Float -> Task = Task 'name
           (reference_expression
             (simple_name_identifier))))))
   (function_definition
-    (definition_info)
+    (definition_info
+      (info))
     (simple_name_identifier)
     (argument_name_identifier)
     (argument_name_identifier)
@@ -987,7 +1004,8 @@ arg_deduction_example 'name 'duration : <- String <- Float -> Task = Task 'name
           (reference_expression
             (simple_name_identifier))))))
   (function_definition
-    (definition_info)
+    (definition_info
+      (info))
     (simple_name_identifier)
     (type
       (simple_type_identifier))
@@ -1006,7 +1024,8 @@ arg_deduction_example 'name 'duration : <- String <- Float -> Task = Task 'name
       (name_expression
         (simple_name_identifier))))
   (function_definition
-    (definition_info)
+    (definition_info
+      (info))
     (simple_name_identifier)
     (argument_name_identifier)
     (type
@@ -1018,7 +1037,8 @@ arg_deduction_example 'name 'duration : <- String <- Float -> Task = Task 'name
         (name_expression
           (simple_name_identifier)))))
   (function_definition
-    (definition_info)
+    (definition_info
+      (info))
     (simple_name_identifier)
     (argument_name_identifier)
     (argument_name_identifier)
@@ -1036,7 +1056,8 @@ arg_deduction_example 'name 'duration : <- String <- Float -> Task = Task 'name
       (annotation_identifier)
       (argument_name_identifier)))
   (function_definition
-    (definition_info)
+    (definition_info
+      (info))
     (simple_name_identifier)
     (argument_name_identifier)
     (argument_name_identifier)
@@ -1052,7 +1073,8 @@ arg_deduction_example 'name 'duration : <- String <- Float -> Task = Task 'name
       (argument_name_identifier)
       (argument_name_identifier)))
   (typeclass_definition
-    (definition_info)
+    (definition_info
+      (info))
     (typeclass_identifier)
     (typeclass_identifier)
     (function_definition
@@ -1060,4 +1082,52 @@ arg_deduction_example 'name 'duration : <- String <- Float -> Task = Task 'name
       (type
         (simple_type_identifier))
       (type
-        (simple_type_identifier)))))
+        (simple_type_identifier))))
+  (function_definition
+    (definition_info
+      (info))
+    (simple_name_identifier)
+    (argument_name_identifier)
+    (match
+      (name_expression
+        (argument_name_identifier))
+      (case
+        (suffix_expression
+          (placeholder))
+        (name_expression
+          (simple_name_identifier)
+          (string_literal)))
+      (case
+        (placeholder)
+        (name_expression
+          (simple_name_identifier)
+          (string_literal)))))
+  (function_definition
+    (definition_info
+      (info))
+    (simple_name_identifier)
+    (type
+      (simple_type_identifier))
+    (block
+      (match
+        (name_definition
+          (simple_name_identifier))
+        (case
+          (name_expression
+            (type
+              (simple_type_identifier))
+            (simple_name_identifier))))
+      (match
+        (suffix_expression
+          (name_definition
+            (simple_name_identifier)))
+        (case
+          (name_expression
+            (type
+              (simple_type_identifier))
+            (simple_name_identifier)
+            (simple_name_identifier))))
+      (name_expression
+        (simple_name_identifier))
+      (return
+        (unit_literal)))))
diff --git a/grammar.js b/grammar.js
index bcaf09a..4648076 100644
--- a/grammar.js
+++ b/grammar.js
@@ -59,7 +59,7 @@ module.exports = grammar({
         optional($.annotation_identifier),
         optional($._reference),
         $.argument_name_identifier,
-        optional('?'),
+        optional($._optional_result),
       )),
       optional(seq(':', repeat1(seq(
         optional($.annotation_identifier),
@@ -149,7 +149,7 @@ module.exports = grammar({
 
     reference_expression: $ => prec(-1, seq($._reference, $._scoped_expression)),
 
-    suffix_expression: $ => seq($._scoped_expression, choice('?', '!')),
+    suffix_expression: $ => seq($._scoped_expression, $._optional_result),
 
     // --- other
 
@@ -232,14 +232,16 @@ module.exports = grammar({
     type: $ => seq(
       optional('^'),
       field('name', $._type_identifier),
-      optional('?'),
+      optional($._optional_result),
       optional(seq('[', repeat1($.type), ']'))
     ),
 
     // --- comments
 
-    definition_info: $ => repeat1(seq(': ', /[^\n]*/)),
-    annotation_info: $ => seq($.annotation_identifier, /[^\n]*/),
+    definition_info: $ => repeat1(seq(': ', $.info)),
+    annotation_info: $ => seq($.annotation_identifier, $.info),
+
+    info: $ => /[^\n]*/,
 
     _exec_comment: $ => token(seq('#!', /[^\n]*/)),
     _line_comment: $ => token(seq('//', /[^\n]*/)),
@@ -249,6 +251,7 @@ module.exports = grammar({
 
     _do: $ => choice('=>', 'do'),
     _var_let: $ => choice(choice('%', 'let'), choice('$', 'var')),
+    _optional_result: $ => choice('?', '!'),
     _reference: $ => choice(choice('->', 'out'), choice('<-', 'in'), choice('<>', 'ref')),
 
     _name_identifier: $ => choice($.argument_name_identifier, $.simple_name_identifier),