From 59c74f79255a713a633fc6b7ca3e18ff89d018b7 Mon Sep 17 00:00:00 2001
From: dos-reis <gdr@axiomatics.org>
Date: Wed, 12 Dec 2007 05:18:09 +0000
Subject: 	* syntax.spad (nil?$Syntax): New predicate.

---
 src/algebra/syntax.spad | 6 ++++++
 1 file changed, 6 insertions(+)

(limited to 'src/algebra/syntax.spad')

diff --git a/src/algebra/syntax.spad b/src/algebra/syntax.spad
index 80bee21e..df62adb5 100644
--- a/src/algebra/syntax.spad
+++ b/src/algebra/syntax.spad
@@ -83,6 +83,9 @@ Syntax(): Public == Private where
     buildSyntax: (%, List %) -> %
       ++ buildSyntax(op, [a1, ..., an]) builds a syntax object for op(a1,...,an).
 
+    nil?: % -> Boolean
+      ++ nil?(s) is true when `s' is a syntax for the constant nil.
+
     getOperator: % -> Union(Integer, DoubleFloat, Symbol, String, %)
       ++ getOperator(x) returns the operator, or tag, of the syntax `x'.
       ++ The return value is itself a syntax if `x' really is an 
@@ -147,6 +150,9 @@ Syntax(): Public == Private where
     buildSyntax(op: %, l: List %): % ==
       cons(op, l) pretend %
 
+    nil? x ==
+      null? rep x
+
     getOperator x ==
       atom? rep x => userError "atom as operand to getOperator"
       s := car rep x
-- 
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