From 3d7fa885768575f03bbd661cd266ccaf346eaf42 Mon Sep 17 00:00:00 2001
From: Joe Marshall <jmarshall@alum.mit.edu>
Date: Tue, 9 Feb 2010 10:01:25 -0800
Subject: [PATCH] Add IGNORABLE declaration for variables.  Issue warning if
 variable is IGNORE, but used anyway.

---
 src/sf/cgen.scm   |  3 +++
 src/sf/object.scm |  3 ++-
 src/sf/pardec.scm | 16 +++++++++++++++-
 src/sf/subst.scm  |  5 +++--
 4 files changed, 23 insertions(+), 4 deletions(-)

diff --git a/src/sf/cgen.scm b/src/sf/cgen.scm
index 7cb7fb8a5..f81e6f3ce 100644
--- a/src/sf/cgen.scm
+++ b/src/sf/cgen.scm
@@ -217,6 +217,9 @@ USA.
 
 (define-method/cgen 'REFERENCE
   (lambda (interns expression)
+    (if (variable/must-ignore? (reference/variable expression))
+	(warn "Variable declared IGNORE, but was used: " 
+	      (variable/name (reference/variable expression))))
     (cgen/variable interns (reference/variable expression))))
 
 (define-method/cgen 'SEQUENCE
diff --git a/src/sf/object.scm b/src/sf/object.scm
index 79fbc1120..4b86532cc 100644
--- a/src/sf/object.scm
+++ b/src/sf/object.scm
@@ -196,7 +196,8 @@ USA.
 (define-flag SIDE-EFFECTED variable/side-effected variable/side-effect!)
 (define-flag REFERENCED    variable/referenced    variable/reference!)
 (define-flag INTEGRATED    variable/integrated    variable/integrated!)
-(define-flag CAN-IGNORE    variable/can-ignore?   variable/can-ignore!)
+(define-flag MAY-IGNORE    variable/may-ignore?   variable/may-ignore!)
+(define-flag MUST-IGNORE   variable/must-ignore?  variable/must-ignore!)
 
 (define open-block/value-marker
   ;; This must be an interned object because we will fasdump it and
diff --git a/src/sf/pardec.scm b/src/sf/pardec.scm
index c4451d75d..5b2694b8f 100644
--- a/src/sf/pardec.scm
+++ b/src/sf/pardec.scm
@@ -306,11 +306,25 @@ USA.
 
 ;;;; Flag Declarations
 
+;; IGNORABLE suppresses warnings about the variable not being used.
+;; This is useful in macros that bind variables that the body may
+;; not actually use.  Mentioning the variable in a sequence will
+;; have the effect of marking it ignorable.
+(define-declaration 'IGNORABLE
+  (lambda (block names)
+    (for-each (lambda (variable)
+		(if variable
+		    (variable/may-ignore! variable)))
+	      (block/lookup-names block names #f))
+    '()))
+
+;; IGNORE causes warnings if an ignored variable actually ends
+;; up being used.
 (define-declaration 'IGNORE
   (lambda (block names)
     (for-each (lambda (variable)
 		(if variable
-		    (variable/can-ignore! variable)))
+		    (variable/must-ignore! variable)))
 	      (block/lookup-names block names #f))
     '()))
 
diff --git a/src/sf/subst.scm b/src/sf/subst.scm
index 5fb5f3421..dfac87893 100644
--- a/src/sf/subst.scm
+++ b/src/sf/subst.scm
@@ -219,7 +219,8 @@ USA.
 (define (variable/unreferenced? variable)
   (and (not (variable/integrated variable))
        (not (variable/referenced variable))
-       (not (variable/can-ignore? variable))))
+       (not (variable/may-ignore? variable))
+       (not (variable/must-ignore? variable))))
 
 (define-method/integrate 'PROCEDURE
   (lambda (operations environment procedure)
@@ -588,7 +589,7 @@ USA.
 	(cons (cond ((reference? action)
 		     ;; This clause lets you ignore a variable by
 		     ;; mentioning it in a sequence.
-		     (variable/can-ignore! (reference/variable action))
+		     (variable/may-ignore! (reference/variable action))
 		     action)
 		    ((eq? action open-block/value-marker)
 		     action)
-- 
2.25.1