From 8c47810df65c610513d4be825bd6ee9a56f97f9f Mon Sep 17 00:00:00 2001
From: dos-reis <gdr@axiomatics.org>
Date: Wed, 9 Mar 2011 23:54:10 +0000
Subject: 	* algebra/catdef.spad.pamphlet (StepThrough) [nextItem]: Now 
 return Maybe %. 	* algebra/ffcat.spad.pamphlet: Propagate change. 
 * algebra/fmod.spad.pamphlet: Likewise. 	*
 algebra/fraction.spad.pamphlet: Likewise. 	*
 algebra/integer.spad.pamphlet: Likewise. 	* algebra/pfbr.spad.pamphlet:
 Likewise. 	* algebra/polycat.spad.pamphlet: Likewise. 	*
 algebra/si.spad.pamphlet: Likewise.

---
 src/algebra/polycat.spad.pamphlet | 20 ++++++++++----------
 1 file changed, 10 insertions(+), 10 deletions(-)

(limited to 'src/algebra/polycat.spad.pamphlet')

diff --git a/src/algebra/polycat.spad.pamphlet b/src/algebra/polycat.spad.pamphlet
index 8931a6de..499b3903 100644
--- a/src/algebra/polycat.spad.pamphlet
+++ b/src/algebra/polycat.spad.pamphlet
@@ -842,25 +842,25 @@ UnivariatePolynomialCategory(R:Ring): Category ==
 
     if R has StepThrough then
        init() == init()$R::%
-       nextItemInner: % -> Union(%,"failed")
+       nextItemInner: % -> Maybe %
        nextItemInner(n) ==
-         zero? n => nextItem(0$R)::R::% -- assumed not to fail
+         zero? n => just(nextItem(0$R)::R::%) -- assumed not to fail
          zero? degree n =>
            nn:=nextItem leadingCoefficient n
-           nn case "failed" => "failed"
-           nn::R::%
+           nn case nothing => nothing
+           just(nn::R::%)
          n1:=reductum n
          n2:=nextItemInner n1 -- try stepping the reductum
-         n2 case % => monomial(leadingCoefficient n,degree n) + n2
+         n2 case % => just(monomial(leadingCoefficient n,degree n) + n2)
          1+degree n1 < degree n => -- there was a hole between lt n and n1
-           monomial(leadingCoefficient n,degree n)+
-             monomial(nextItem(init()$R)::R,1+degree n1)
+           just(monomial(leadingCoefficient n,degree n)+
+             monomial(nextItem(init()$R)::R,1+degree n1))
          n3:=nextItem leadingCoefficient n
-         n3 case "failed" => "failed"
-         monomial(n3,degree n)
+         n3 case nothing => nothing
+         just monomial(n3,degree n)
        nextItem(n) ==
          n1:=nextItemInner n
-         n1 case "failed" => monomial(nextItem(init()$R)::R,1+degree(n))
+         n1 case nothing => just monomial(nextItem(init()$R)::R,1+degree(n))
          n1
 
     if R has GcdDomain then
-- 
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