-Functions returning plain strings and lists of strings.
-function (foo, bar) returning string = { echo hello }
-function (foo, bar) returning strings = { echo hello; echo goodbye }
-Then re-add the sort function.
+Infinite loop when you have this goal:
+goal pod2man (page, section) = "docs/%page.%section" : "docs/%page.pod" { ... }
+This is caused by %section matching "pod" so the rule is called
+again, even if the local file docs/%page.pod actually exists.
+
+Implement make-like “eval” function (similar to include directive,
+but it evaluates the output of a function as Goalfile syntax).
+
+Implement make-like “origin” function. This is easy but it requires
+us to track to the origin of definitions which we do not do at
+the moment.