add module testing

Also fix module import

tests/modules/Makefile

@@ -0,0 +1,28 @@
+# Multi-module linking.
+#
+# Modules are only testable end to end, and nothing else in the suite
+# links more than one translation unit. Three things have to hold at
+# once: an imported `pub fn' comes out as a prototype with external
+# linkage, an imported `pub var' as an extern declaration, and the
+# module's object survives being passed after `--'. Get any of them
+# wrong and this fails to link -- or, in the `pub var' case, links and
+# quietly counts into a private copy.
+
+SEXC ?= ../../sexc
+
+EXPECTED = hello, world\nhello, sex\n2 greetings
+
+check:
+	@$(SEXC) greet.sex -c -o greet.o
+	@$(SEXC) greet-app.sex -o greet-app -- greet.o
+	@if [ "`./greet-app`" = "`printf '$(EXPECTED)\n'`" ]; then \
+		echo "modules ok"; \
+	else \
+		echo "modules FAILED, got:"; ./greet-app; $(MAKE) clean; exit 1; \
+	fi
+	@$(MAKE) --no-print-directory clean
+
+clean:
+	@rm -f greet.o greet-app
+
+.PHONY: check clean

tests/modules/greet-app.sex

@@ -0,0 +1,19 @@
+;;; Uses the greet module. Build both, then link them:
+;;;
+;;;   ./sexc example/greet.sex -c -o greet.o
+;;;   ./sexc example/greet-app.sex -o greet-app -- greet.o
+;;;
+;;; `(import greet)' pastes greet's public declarations here: `greet'
+;;; as a prototype and `greet-count' as an extern. Both keep external
+;;; linkage, so they refer to the one definition in greet.o rather than
+;;; to private copies.
+
+(include stdio.h)
+
+(import greet)
+
+(pub fn main () int
+  (greet "world")
+  (greet "sex")
+  (printf "%d greetings\n" greet-count)
+  (return 0))

tests/modules/greet.sex

@@ -0,0 +1,18 @@
+;;; A module. Everything marked `pub' forms its public interface;
+;;; everything else is private to this file.
+;;;
+;;; Importing a module does not link it: it pastes the declarations, so
+;;; the compiled object still has to be handed to the C compiler. See
+;;; greet-app.sex.
+
+(include stdio.h)
+
+(pub var greet-count int 0)
+
+(pub fn greet ((name (* const char))) void
+  (++ greet-count)
+  (printf "hello, %s\n" name))
+
+;;; Not `pub': invisible to importers, and static in the generated C.
+(fn unused-helper () void
+  (printf "private\n"))