Added structure GC

Clean up doc

scsh/interaction/README

@@ -1,3 +1,14 @@
+The interaction library currently offers three structures that provide
+a programmatic interface to Scheme 48's debugging facilities: 
+
+* REPLS starts the read-eval-print-loop with arbitrary input and
+  output ports.
+
+* INSPECT-EXCEPTION provides exception handlers that allow interactive
+  inspection of exceptions and their backtrace.
+
+* GC provides a small run-time interface to the garbage collector.
+
 The structure REPLS offers procedures to start up the
 read-eval-print-loop (REPL) from a script.
 
@@ -28,6 +39,9 @@ from the socket's output port and prints it to
 (current-output-port).
 
 
+The structure INSPECT-EXCEPTION makes some of the functionality of the
+,debug and ,preview commands available.
+
 (with-inspecting-handler port prepare thunk)
 
 This procedure installs a exception handler which captures all
@@ -107,3 +121,17 @@ The procedural analogy to the ,proceed command. Continuation must be a
 continuation object as captured by
 WITH-FATAL-AND-CAPTURING-ERROR-HANDLER, not a procedure as captured by
 CALL-WITH-CURRENT-CONTINUATION.
+
+
+The structure GC provides a procedure equivalent to the ,collect
+command and offers some statistics about the garbage collector.
+
+(collect outport) -> unspecified
+
+Invokes the GC and prints the number of free words before and after
+the collection to OUTPORT.
+
+(gc-count) -> number
+
+Returns the number of times the garbage collector has been invoked
+since the start of the system.

scsh/interaction/gc.scm

@@ -0,0 +1,15 @@
+(define (collect port)
+  (let ((before (memory-status (enum memory-status-option available) #f)))
+    (primitive-collect)
+    (let ((after (memory-status (enum memory-status-option available) #f)))
+      (display "Before: " port)
+      (write before port)
+      (display " words free in semispace" port)
+      (newline port)
+      (display "After:  " port)
+      (write after port)
+      (display " words free in semispace" port)
+      (newline port))))
+
+(define (gc-count)
+  (memory-status (enum memory-status-option gc-count) #f))

scsh/interaction/packages.scm

@@ -10,6 +10,10 @@
 (define-interface socket2stdports-interface
   (export socket<->stdports))
 
+(define-interface gc-interface
+  (export collect
+          gc-count))
+
 (define-structure repls repls-interface
   (open scheme-with-scsh
 	command-levels
@@ -35,3 +39,12 @@
 	handle
 	threads)
   (files socket2stdport))
+
+(define-structure gc gc-interface
+  (open scheme
+        enumerated
+        (subset architecture (memory-status-option))
+        (modify primitives (rename (collect primitive-collect))
+                           (expose collect memory-status))
+        threads)
+  (files gc))