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, 11 insertions, 5 deletions

diff --git a/src/aup.h b/src/aup.h
index 75047af..98b59b0 100644
--- a/src/aup.h
+++ b/src/aup.h
@@ -4,16 +4,22 @@
 #include <stddef.h>
 
 /* aup: source text to a Pure module (Pure docs/design/008-module-format.md). */
-enum { AUP_SOURCE_LIMIT = 32768, AUP_MESSAGE = 160 };
+enum { AUP_SOURCE_LIMIT = 32768, AUP_MESSAGE = 256, AUP_PATH = 256 };
 
 typedef struct {
+    char path[AUP_PATH]; /* the library the error is in, or "" for the main source */
     int line, column;
     char message[AUP_MESSAGE];
 } AupDiagnostic;
 
+/* Finds the library that `use name` names: its source, alive until
+ * aup_compile returns, and a path that diagnostics show. */
+typedef bool (*AupLoad)(void *context, const char *name, const char **source, size_t *length,
+                        char path[AUP_PATH]);
+
 /* Compile source into a newly allocated module (free with free()). The same
- * source always produces the same bytes. On failure *module is NULL and the
- * diagnostic names the first error. */
-bool aup_compile(const char *source, size_t length, unsigned char **module, size_t *size,
-                 AupDiagnostic *error);
+ * sources always produce the same bytes. On failure *module is NULL and the
+ * diagnostic names the first error. load may be NULL when nothing is used. */
+bool aup_compile(const char *source, size_t length, AupLoad load, void *context,
+                 unsigned char **module, size_t *size, AupDiagnostic *error);
 #endif