Add fns and libraries

fn name(params) = value declares one expression, inlined where it is
called: arguments are computed once onto the stack and the body reads them
with PICK, so a fn costs no runtime call and keeps Pure's bound on work.
Parameters take any kind of value; recursion is a compile error.

use name reads name.aup beside the source or from AUP_PATH. A library
declares only fns and uses, sees only its parameters, and is called as
name.fn(...). Diagnostics now carry the file they are in, and the
compiler takes a loader so that sources come from the host.

examples/words.aup is such a library; examples/tasks.aup uses it and still
matches its reference model.

1 files changed, 5 insertions, 0 deletions

diff --git a/examples/words.aup b/examples/words.aup
new file mode 100644
index 0000000..2bfc0a5
--- /dev/null
+++ b/examples/words.aup
@@ -0,0 +1,5 @@
+# Words for counts and marks. A library: only fns, no state, so any app can
+# `use words` and call words.counted(...).
+fn plural(count, one, many) = if count == 1 { one } else { many }
+fn counted(count, one, many) = "{count} {plural(count, one, many)}"
+fn check(done) = if done { "x" } else { " " }