add generics

test/fixtures/valid/pipelines.ls

@@ -15,9 +15,9 @@ commented := 'value' # an inline comment preserves continuation
 computed := 1 + 2
 ->to_str
 
-fallible: i32 -> i32 ! Error: @ value: i32 { ok value }
+fallible: i32 -> i32 ! Error: @ value: i32 { value->|.ok }
 
 propagate: i32 -> i32 ! Error: @ value: i32 {
     result := {value->fallible}?
-    ok result
+    result->|.ok
 }