implement closures

tests/modules/Makefile

@@ -10,14 +10,17 @@
 #
 # It also checks what only a second translation unit can check: that an
 # imported type reaches the type database, by expanding a macro that
-# reads the imported struct's fields.
+# reads the imported struct's fields; and that a closure type crossing
+# the boundary works both ways -- one built in the module and called
+# here, one built here and called there, through a code pointer that is
+# static in the other object.
 #
 # The public forms carry comments in their headers, which the reduction
 # to a prototype and to an extern both have to look past.
 
 SEXC ?= ../../sexc
 
-EXPECTED = hello, world\nhello, sex\n2 greetings\ntext times \ntext times \nmood 1
+EXPECTED = hello, world\nhello, sex\n2 greetings\ntext times \ntext times \nmood 1\nclosure 15 21 201
 
 check:
 	@$(SEXC) greet.sex -c -o greet.o

tests/modules/greet-app.sex

@@ -26,4 +26,11 @@
   (printf "\n")
   (var m (enum mood) grumpy)
   (printf "mood %d\n" m)
+
+  (var add-10 (closure ((int)) int) (make-adder 10))
+  (printf "closure %d %d" (add-10 5) (apply-twice add-10 1))
+  (var base int 100)
+  (var here (closure ((int)) int)
+       (closure ((x int)) int (base) (return (+ base x))))
+  (printf " %d\n" (apply-twice here 1))
   (return 0))

tests/modules/greet.sex

@@ -35,6 +35,19 @@
   (++ greet-count)
   (printf "hello, %s\n" name))
 
+;;; A closure type crossing the boundary. Both units generate the
+;;; struct for this signature independently, so they have to agree on
+;;; its tag and its layout, or the value is passed wrong and nothing
+;;; says so.
+(pub fn make-adder ((n int)) (closure ((int)) int)
+  (return (closure ((b int)) int (n)
+            (return (+ n b)))))
+
+;;; The other direction: a closure built by the importer, whose code
+;;; pointer is static in *its* object, called from here
+(pub fn apply-twice ((f (closure ((int)) int)) (x int)) int
+  (return (f (f x))))
+
 ;;; Not `pub': invisible to importers, and static in the generated C.
 (fn unused-helper () void
   (printf "private\n"))