help.lint.checks: improve check-example to print the stack (if any).

Any output from the example will be preserved like it currently is,
and any objects on the stack will be printed the same way they are
in the listener prefixed by ``--- Data stack:``.

basis/help/lint/checks/checks.factor

@@ -1,10 +1,11 @@
 ! Copyright (C) 2009 Slava Pestov.
 ! See http://factorcode.org/license.txt for BSD license.
 USING: accessors arrays assocs classes classes.struct
-classes.tuple combinators combinators.short-circuit debugger
+classes.tuple combinators combinators.short-circuit
-definitions effects eval formatting fry grouping help
+combinators.smart continuations debugger definitions effects
-help.markup help.topics io io.streams.string kernel macros math
+eval formatting fry grouping help help.markup help.topics io
-namespaces sequences sequences.deep sets splitting strings
+io.streams.string kernel macros math namespaces parser.notes
+prettyprint sequences sequences.deep sets splitting strings
 summary tools.destructors unicode vocabs vocabs.loader words
 words.constant words.symbol ;
 IN: help.lint.checks
@@ -28,12 +29,23 @@ SYMBOL: vocab-articles
         } member?
     ] reject ;
 
+: eval-with-stack ( str -- output )
+    [
+        [
+            parser-quiet? on parse-string [
+                output>array [
+                    nl "--- Data stack:" print stack.
+                ] unless-empty
+            ] call( quot -- )
+        ] [ nip print-error ] recover
+    ] with-string-writer ;
+
 : check-example ( element -- )
     [
         '[
             _ rest [
                 but-last "\n" join
-                [ (eval>string) ] call( code -- output )
+                eval-with-stack
                 "\n" ?tail drop
             ] keep
             last assert=