* algebra/any.spad.pamphlet (Maybe): New domain.

	* algebra/exposed.lsp.pamphlet: Expose it.
	* algebra/Makefile.pamphlet (axiom_algebra_layer_1): Include MAYBE.

4 files changed, 54 insertions, 5 deletions

diff --git a/src/algebra/Makefile.in b/src/algebra/Makefile.in
index 14a4c8db..d0169a63 100644
--- a/src/algebra/Makefile.in
+++ b/src/algebra/Makefile.in
@@ -376,7 +376,7 @@ axiom_algebra_layer_1 = \
   PATAB    PPCURVE  PSCURVE  REAL     RESLATC   RETRACT  \
   RETRACT- SEGCAT   BINDING  SYNTAX   BMODULE   LOGIC    \
   LOGIC-   EVALAB   EVALAB-  FEVALAB  FEVALAB-  BYTE     \
-  OSGROUP
+  OSGROUP  MAYBE
 
 axiom_algebra_layer_1_nrlibs = \
 	$(addsuffix .NRLIB/code.$(FASLEXT),$(axiom_algebra_layer_1))
diff --git a/src/algebra/Makefile.pamphlet b/src/algebra/Makefile.pamphlet
index c2f97a52..7170fa32 100644
--- a/src/algebra/Makefile.pamphlet
+++ b/src/algebra/Makefile.pamphlet
@@ -219,7 +219,7 @@ axiom_algebra_layer_1 = \
   PATAB    PPCURVE  PSCURVE  REAL     RESLATC   RETRACT  \
   RETRACT- SEGCAT   BINDING  SYNTAX   BMODULE   LOGIC    \
   LOGIC-   EVALAB   EVALAB-  FEVALAB  FEVALAB-  BYTE     \
-  OSGROUP
+  OSGROUP  MAYBE
 
 axiom_algebra_layer_1_nrlibs = \
 	$(addsuffix .NRLIB/code.$(FASLEXT),$(axiom_algebra_layer_1))
diff --git a/src/algebra/any.spad.pamphlet b/src/algebra/any.spad.pamphlet
index e0e93817..af9c3f2e 100644
--- a/src/algebra/any.spad.pamphlet
+++ b/src/algebra/any.spad.pamphlet
@@ -1,14 +1,16 @@
 \documentclass{article}
 \usepackage{axiom}
 \begin{document}
-\title{\$SPAD/src/algebra any.spad}
-\author{Robert S. Sutor}
+\title{src/algebra any.spad}
+\author{Robert S. Sutor \and Gabriel Dos~Reis}
 \maketitle
+
 \begin{abstract}
 \end{abstract}
-\eject
+
 \tableofcontents
 \eject
+
 \section{domain NONE None}
 <<domain NONE None>>=
 )abbrev domain NONE None
@@ -31,6 +33,50 @@ None():SetCategory == add
     x:% = y:% == EQ(x,y)$Lisp
 
 @
+
+
+\section{The Maybe domain}
+<<domain MAYBE Maybe>>=
+)abbrev domain MAYBE Maybe
+++ Author: Gabriel Dos Reis
+++ Date Created: August 20, 2008
+++ Also See: Union(T,"failed")
+++ Description:
+++   This domain implements the notion of optional vallue, where
+++   a computation may fail to produce expected value.
+++ Note: Ideally, this domain definition should be a one-liner.
+++       That is currently impossible because of mismatch between
+++       the `old representation' and `new representation' for domains.
+Maybe(T: CoercibleTo OutputForm): Public == Private where
+  Public == Join(UnionType,CoercibleTo OutputForm) with
+    _case: (%,[| T |]) -> Boolean
+      ++ x case T returns true if x is actually a data of type T.
+    _case: (%,[| nothing |]) -> Boolean
+      ++ x case nothing evaluates true if the value for x is missing.
+    coerce: T -> % 
+      ++ x::T injects the value x into %.
+    coerce: % -> T
+      ++ x::T tries to extract the value of T from the computation x.
+      ++ Produces a runtime error when the computation fails.
+    autoCoerce: % -> T
+      ++ same as above but implicitly called by the compiler.
+    nothing: %
+      ++ represents failure.
+  Private == add
+    Rep == Union(T,"nothing")
+    nothing == per("nothing"::Rep)
+    coerce(x: T): % == per(x::Rep)
+    coerce(x: %): T == rep(x)::T
+    autoCoerce x == rep(x)::T
+    x case T == rep x case T
+    x case nothing == rep x case "nothing"
+    coerce(x: %): OutputForm == 
+      x case T => x::T::OutputForm
+      paren(empty()$OutputForm)$OutputForm
+@
+
+
+
 \section{package NONE1 NoneFunctions1}
 <<package NONE1 NoneFunctions1>>=
 )abbrev package NONE1 NoneFunctions1
@@ -57,6 +103,7 @@ NoneFunctions1(S:Type): Exports == Implementation where
     coerce(s:S):None == s pretend None
 
 @
+
 \section{domain ANY Any}
 <<domain ANY Any>>=
 )abbrev domain ANY Any
@@ -473,6 +520,7 @@ Environment(): Public == Private where
 -- may be Any.
 
 <<domain NONE None>>
+<<domain MAYBE Maybe>>
 <<package NONE1 NoneFunctions1>>
 <<domain ANY Any>>
 <<package ANY1 AnyFunctions1>>
diff --git a/src/algebra/exposed.lsp.pamphlet b/src/algebra/exposed.lsp.pamphlet
index 2dec4c37..f9ba341c 100644
--- a/src/algebra/exposed.lsp.pamphlet
+++ b/src/algebra/exposed.lsp.pamphlet
@@ -222,6 +222,7 @@
   (|MatrixCategoryFunctions2| . MATCAT2)
   (|MatrixCommonDenominator| . MCDEN)
   (|MatrixLinearAlgebraFunctions| . MATLIN)
+  (|Maybe| . MAYBE)
   (|MergeThing| . MTHING)
   (|ModularDistinctDegreeFactorizer| . MDDFACT)
   (|ModuleOperator| . MODOP)