\documentclass{article}
\usepackage{axiom}
\begin{document}
\title{\$SPAD/src/interp cstream.boot}
\author{The Axiom Team}
\maketitle
\begin{abstract}
\end{abstract}
\eject
\tableofcontents
\eject
The input stream is parsed into a large s-expression by repeated calls
to Delay. Delay takes a function f and an argument x and returns a list
consisting of ("nonnullstream" f x). Eventually multiple calls are made
and a large list structure is created that consists of 
("nonnullstream" f x ("nonnullstream" f1 x1 ("nonnullstream" f2 x2...

This delay structure is given to StreamNull which walks along the
list looking at the head. If the head is "nonnullstream" then the
function is applied to the argument.

So, in effect, the input is "zipped up" into a Delay data structure
which is then evaluated by calling StreamNull. This "zippered stream"
parser was a research project at IBM and Axiom was the testbed (which
explains the strange parsing technique).
\section{License}
<<license>>=
-- Copyright (c) 1991-2002, The Numerical ALgorithms Group Ltd.
-- All rights reserved.
--
-- Redistribution and use in source and binary forms, with or without
-- modification, are permitted provided that the following conditions are
-- met:
--
--     - Redistributions of source code must retain the above copyright
--       notice, this list of conditions and the following disclaimer.
--
--     - Redistributions in binary form must reproduce the above copyright
--       notice, this list of conditions and the following disclaimer in
--       the documentation and/or other materials provided with the
--       distribution.
--
--     - Neither the name of The Numerical ALgorithms Group Ltd. nor the
--       names of its contributors may be used to endorse or promote products
--       derived from this software without specific prior written permission.
--
-- THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
-- IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
-- TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
-- PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER
-- OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
-- EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
-- PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
-- PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
-- LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
-- NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
-- SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

@
<<*>>=
<<license>>

)package "BOOT"

--% Stream Utilities
 
npNull x== StreamNull x
 
StreamNull x==
  null x or EQCAR (x,"nullstream") => true
  while EQCAR(x,"nonnullstream") repeat
          st:=APPLY(CADR x,CDDR x)
          RPLACA(x,CAR st)
          RPLACD(x,CDR st)
  EQCAR(x,"nullstream")
 
Delay(f,x)==cons("nonnullstream",[f,:x])
 
StreamNil:= ["nullstream"]
 
incRgen s==Delay(function incRgen1,[s])
 
incRgen1(:z)==
        [s]:=z
        a:=shoeread_-line s
        if NULL a
        then (CLOSE s;StreamNil)

        else cons(a,incRgen s)
 
incIgen n==Delay(function incIgen1,[n])
incIgen1(:z)==
        [n]:=z
        n:=n+1
        cons(n,incIgen n)
 
incZip(g,f1,f2)==Delay(function incZip1,[g,f1,f2])
incZip1(:z)==
     [g,f1,f2]:=z
     StreamNull f1 => StreamNil
     StreamNull f2 => StreamNil
     cons(FUNCALL(g,car f1,car f2),incZip(g,cdr f1,cdr f2))
 
incAppend(x,y)==Delay(function incAppend1,[x,y])
 
incAppend1(:z)==
     [x,y]:=z
     if StreamNull x
     then if StreamNull y
          then StreamNil
          else y
     else cons(car x,incAppend(cdr x,y))
 
next(f,s)==Delay(function next1,[f,s])
next1(:z)==
      [f,s]:=z
      StreamNull s=> StreamNil
      h:= APPLY(f, [s])
      incAppend(car h,next(f,cdr h))
 
nextown(f,g,s)==Delay(function nextown1,[f,g,s])
nextown1 (:z)==
      [f,g,s]:=z
      StreamNull s=>
           spadcall1 g
           StreamNil
      StreamNull s
      h:=spadcall2 (f, s)
      incAppend(car h,nextown(f,g,cdr h))
 
nextown2(f,g,e,x)==nextown(cons(f,e),cons(g,e),x)
 
spadcall1(g)==
    [impl, :env] := g
    APPLY(impl, [env])
 
spadcall2(f,args) ==
    [impl, :env] := f
    APPLY(impl, [args, env])
@
\eject
\begin{thebibliography}{99}
\bibitem{1} nothing
\end{thebibliography}
\end{document}