Add function binding to error message

crates/reporting/src/error/parse.rs

@@ -290,7 +290,10 @@ fn to_expr_report<'a>(
                                 ])
                                 .indent(4),
                             alloc.reflow("And to define a function:"),
-                            alloc.reflow("increment = \\n -> n + 1").indent(4),
+                            alloc.vcat(vec![
+                                alloc.text("increment : I64 -> I64"),
+                                alloc.text("increment = \\n -> n + 1"),
+                            ]).indent(4)
                         ])]
                     }
                 },

crates/reporting/tests/test_reporting.rs

@@ -5653,6 +5653,7 @@ All branches in an `if` must have the same type!
 
     And to define a function:
 
+        increment : I64 -> I64
         increment = \n -> n + 1
 
     "###