\documentclass{article}
\usepackage{open-axiom}
\begin{document}
\title{\$SPAD/src/algebra stream.spad}
\author{Clifton J. Williamson, William Burge, Stephen M. Watt}
\maketitle

\begin{abstract}
\end{abstract}

\tableofcontents
\eject

\section{category LZSTAGG LazyStreamAggregate}
<<category LZSTAGG LazyStreamAggregate>>=
import Type
import Boolean
import NonNegativeInteger
)abbrev category LZSTAGG LazyStreamAggregate
++ Category of streams with lazy evaluation
++ Author: Clifton J. Williamson
++ Date Created: 22 November 1989
++ Date Last Updated: 20 July 1990
++ Keywords: stream, infinite list, infinite sequence
++ Description:
++ LazyStreamAggregate is the category of streams with lazy
++ evaluation.  It is understood that the function 'empty?' will
++ cause lazy evaluation if necessary to determine if there are
++ entries.  Functions which call 'empty?', e.g. 'first' and 'rest',
++ will also cause lazy evaluation if necessary.

LazyStreamAggregate(S:Type): Category == StreamAggregate(S) with
  remove: (S -> Boolean,%) -> %
    ++ remove(f,st) returns a stream consisting of those elements of stream
    ++ st which do not satisfy the predicate f.
    ++ Note: \spad{remove(f,st) = [x for x in st | not f(x)]}.
  select: (S -> Boolean,%) -> %
    ++ select(f,st) returns a stream consisting of those elements of stream
    ++ st satisfying the predicate f.
    ++ Note: \spad{select(f,st) = [x for x in st | f(x)]}.
  explicitEntries?: % -> Boolean
    ++ explicitEntries?(s) returns true if the stream s has
    ++ explicitly computed entries, and false otherwise.
  explicitlyEmpty?: % -> Boolean
    ++ explicitlyEmpty?(s) returns true if the stream is an
    ++ (explicitly) empty stream.
    ++ Note: this is a null test which will not cause lazy evaluation.
  lazy?: % -> Boolean
    ++ lazy?(s) returns true if the first node of the stream s
    ++ is a lazy evaluation mechanism which could produce an
    ++ additional entry to s.
  lazyEvaluate: % -> %
    ++ lazyEvaluate(s) causes one lazy evaluation of stream s.
    ++ Caution: the first node must be a lazy evaluation mechanism
    ++ (satisfies \spad{lazy?(s) = true}) as there is no error check.
    ++ Note: a call to this function may
    ++ or may not produce an explicit first entry
  frst: % -> S
    ++ frst(s) returns the first element of stream s.
    ++ Caution: this function should only be called after a \spad{empty?} test
    ++ has been made since there no error check.
  rst: % -> %
    ++ rst(s) returns a pointer to the next node of stream s.
    ++ Caution: this function should only be called after a \spad{empty?} test
    ++ has been made since there no error check.
  numberOfComputedEntries: % -> NonNegativeInteger
    ++ numberOfComputedEntries(st) returns the number of explicitly
    ++ computed entries of stream st which exist immediately prior to the time
    ++ this function is called.
  extend: (%,Integer) -> %
    ++ extend(st,n) causes entries to be computed, if necessary,
    ++ so that 'st' will have at least 'n' explicit entries or so
    ++ that all entries of 'st' will be computed if 'st' is finite
    ++ with length <= n.
  complete: % -> %
    ++ complete(st) causes all entries of 'st' to be computed.
    ++ this function should only be called on streams which are
    ++ known to be finite.

 add

  MIN ==> 1  -- minimal stream index

  I   ==> Integer
  NNI ==> NonNegativeInteger
  L   ==> List
  U   ==> UniversalSegment Integer

  indexx?            : (Integer,%) -> Boolean
  cycleElt           : % -> Union(%,"failed")
  computeCycleLength : % -> NNI
  computeCycleEntry  : (%,%) -> %

--% SETCAT functions

  if S has SetCategory then

    x = y ==
      eq?(x,y) => true
      explicitlyFinite? x and explicitlyFinite? y =>
        entries x = entries y
      explicitEntries? x and explicitEntries? y =>
        frst x = frst y and %peq(rst x,rst y)$Foreign(Builtin)
      -- treat cyclic streams
      false

--% HOAGG functions

  --null x == empty? x

  less?(x,n) ==
    n = 0    => false
    empty? x => true
    less?(rst x,(n-1) :: NNI)

  more?(x,n) ==
    empty? x => false
    n = 0    => true
    more?(rst x,(n-1) :: NNI)

  size?(x,n) ==
    empty? x => n = 0
    size?(rst x,(n-1) :: NNI)

--% FINAGG functions
  if % has FiniteAggregate S then
    # x ==
      -- error if stream is not finite
      y := x
      for i in 0.. repeat
        explicitlyEmpty? y  => return i
        lazy? y => error "#: infinite stream"
        y := rst y
        if odd? i then x := rst x
        eq?(x,y) => error "#: infinite stream"

    any?(f,x) ==
      -- error message only when x is a stream with lazy
      -- evaluation and f(s) = false for all stream elements
      -- 's' which have been computed when the function is
      -- called
      y := x
      for i in 0.. repeat
        explicitlyEmpty? y  => return false
        lazy? y => error "any?: infinite stream"
        f frst y => return true
        y := rst y
        if odd? i then x := rst x
        eq?(x,y) => return false

    every?(f,x) ==
      -- error message only when x is a stream with lazy
      -- evaluation and f(s) = true for all stream elements
      -- 's' which have been computed when the function is
      -- called
      y := x
      for i in 0.. repeat
        explicitlyEmpty? y => return true
        lazy? y => error "every?: infinite stream"
        not f frst y => return false
        y := rst y
        if odd? i then x := rst x
        eq?(x,y) => return true

--  following ops count and member? are only exported if $ has FiniteAggregate S

--  count(f:S -> Boolean,x:%) ==
--    -- error if stream is not finite
--    count : NNI := 0
--    y := x
--    for i in 0.. repeat
--      explicitlyEmpty? y  => return count
--      lazy? y => error "count: infinite stream"
--      if f frst y then count := count + 1
--      y := rst y
--      if odd? i then x := rst x
--      eq?(x,y) => error "count: infinite stream"


--  if S has SetCategory then

--      count(s:S,x:%) == count(#1 = s,x)
--        -- error if stream is not finite

--    member?(s,x) ==
--      -- error message only when x is a stream with lazy
--      -- evaluation and 's' is not among the stream elements
--      -- which have been computed when the function is called
--      y := x
--      for i in 0.. repeat
--        explicitlyEmpty? y  => return false
--        lazy? y => error "member?: infinite stream"
--        frst y = s => return true
--        y := rst y
--        if odd? i then x := rst x
--        eq?(x,y) => return false

  entries x ==
    -- returns a list of elements which have been computed
    -- error if infinite
    y := x
    l : L S := empty()
    for i in 0.. repeat
      explicitlyEmpty? y  => return reverse! l
      lazy? y => error "infinite stream"
      l := concat(frst y,l)
      y := rst y
      if odd? i then x := rst x
      eq?(x,y) => error "infinite stream"

--% CNAGG functions

  construct l ==
    empty? l => empty()
    concat(first l, construct rest l)

  --entries x ==
    -- returns a list of the stream elements
    -- error if the stream is not finite
    --members x

--% ELTAGG functions

  elt(x:%,n:I) ==
    n < MIN or empty? x => error "elt: no such element"
    n = MIN => frst x
    elt(rst x,n - 1)

  elt(x:%,n:I,s:S) ==
    n < MIN or empty? x => s
    n = MIN => frst x
    elt(rst x,n - 1)

--% IXAGG functions

-- following assumes % has FiniteAggregate S and S has SetCategory
--  entry?(s,x) ==
--    -- error message only when x is a stream with lazy
--    -- evaluation and 's' is not among the stream elements
--    -- which have been computed when the function is called
--    member?(s,x)

  --entries x ==
    -- error if the stream is not finite
    --members x

  indexx?(n,x) ==
    empty? x => false
    n = MIN => true
    indexx?(n-1,rst x)

  index?(n,x) ==
    -- returns 'true' iff 'n' is the index of an entry which
    -- may or may not have been computed when the function is
    -- called
    -- additional entries are computed if necessary
    n < MIN => false
    indexx?(n,x)

  indices x ==
    -- error if stream is not finite
    y := x
    l : L I := empty()
    for i in MIN.. repeat
      explicitlyEmpty? y  => return reverse! l
      lazy? y => error "indices: infinite stream"
      l := concat(i,l)
      y := rst y
      if odd? i then x := rst x
      eq?(x,y) => error "indices: infinite stream"

  maxIndex x ==
    -- error if stream is not finite
    empty? x =>
      error "maxIndex: no maximal index for empty stream"
    y := rst x
    for i in MIN.. repeat
      explicitlyEmpty? y  => return i
      lazy? y => error "maxIndex: infinite stream"
      y := rst y
      if odd? i then x := rst x
      eq?(x,y) => error "maxIndex: infinite stream"

  minIndex x ==
    empty? x => error "minIndex: no minimal index for empty stream"
    MIN

--% LNAGG functions

  delete(x:%,n:I) ==
  -- non-destructive
    not index?(n,x) => error "delete: index out of range"
    concat(first(x,(n - MIN) :: NNI), rest(x,(n - MIN + 1) :: NNI))

  delete(x:%,seg:U) ==
    low := lo seg
    hasHi seg =>
      high := hi seg
      high < low => copy x
      (not index?(low,x)) or (not index?(high,x)) =>
        error "delete: index out of range"
      concat(first(x,(low - MIN) :: NNI),rest(x,(high - MIN + 1) :: NNI))
    not index?(low,x) => error "delete: index out of range"
    first(x,(low - MIN) :: NNI)

  elt(x:%,seg:U) ==
    low := lo seg
    hasHi seg =>
      high := hi seg
      high < low => empty()
      (not index?(low,x)) or (not index?(high,x)) =>
        error "elt: index out of range"
      first(rest(x,(low - MIN) :: NNI),(high - low + 1) :: NNI)
    not index?(low,x) => error "elt: index out of range"
    rest(x,(low - MIN) :: NNI)

  insert(s:S,x:%,n:I) ==
    not index?(n,x) => error "insert: index out of range"
    nn := (n - MIN) :: NNI
    concat([first(x,nn), concat(s, empty()), rest(x,nn)])

  insert(y:%,x:%,n:I) ==
    not index?(n,x) => error "insert: index out of range"
    nn := (n - MIN) :: NNI
    concat([first(x,nn), y, rest(x,nn)])

--% RCAGG functions

  cycleElt x == cycleElt(x)$CyclicStreamTools(S,%)

  cyclic? x ==
    cycleElt(x) case "failed" => false
    true

  if S has SetCategory then
    child?(x,y) ==
      empty? y => error "child: no children"
      x = rst y

  children x ==
    empty? x => error "children: no children"
    [rst x]

  distance(x,z) ==
    y := x
    for i in 0.. repeat
      eq?(y,z) => return i
      (explicitlyEmpty? y) or (lazy? y) =>
        error "distance: 2nd arg not a descendent of the 1st"
      y := rst y
      if odd? i then x := rst x
      eq?(x,y) =>
        error "distance: 2nd arg not a descendent of the 1st"

  if S has SetCategory then
    node?(z,x) ==
      -- error message only when x is a stream with lazy
      -- evaluation and 'y' is not a node of 'x'
      -- which has been computed when the function is called
      y := x
      for i in 0.. repeat
        z = y => return true
        explicitlyEmpty? y => return false
        lazy? y => error "node?: infinite stream"
        y := rst y
        if odd? i then x := rst x
        eq?(x,y) => return false

  nodes x ==
    y := x
    l : L % := []
    for i in 0.. repeat
      explicitlyEmpty? y => return reverse! l
      lazy? y => error "nodes: infinite stream"
      l := concat(y,l)
      y := rst y
      if odd? i then x := rst x
      eq?(x,y) => error "nodes: infinite stream"
    l -- @#$%^& compiler

  leaf? x == empty? rest x

  value x == first x

--% URAGG functions

  computeCycleLength cycElt ==
    computeCycleLength(cycElt)$CyclicStreamTools(S,%)

  computeCycleEntry(x,cycElt) ==
    computeCycleEntry(x,cycElt)$CyclicStreamTools(S,%)

  cycleEntry x ==
    cycElt := cycleElt x
    cycElt case "failed" =>
      error "cycleEntry: non-cyclic stream"
    computeCycleEntry(x,cycElt::%)

  cycleLength x ==
    cycElt := cycleElt x
    cycElt case "failed" =>
      error "cycleLength: non-cyclic stream"
    computeCycleLength(cycElt::%)

  cycleTail x ==
    cycElt := cycleElt x
    cycElt case "failed" =>
      error "cycleTail: non-cyclic stream"
    y := x := computeCycleEntry(x,cycElt::%)
    z := rst x
    repeat
      eq?(x,z) => return y
      y := z ; z := rst z

  elt(x,"first") == first x

  first(x,n) ==
  -- former name: take
    n = 0 or empty? x => empty()
    concat(frst x, first(rst x,(n-1) :: NNI))

  rest x ==
    empty? x => error "Can't take the rest of an empty stream."
    rst x

  elt(x,"rest") == rest x

  rest(x,n) ==
  -- former name: drop
    n = 0 or empty? x => x
    rest(rst x,(n-1) :: NNI)

  last x ==
    -- error if stream is not finite
    empty? x => error "last: empty stream"
    y1 := x
    y2 := rst x
    for i in 0.. repeat
      explicitlyEmpty? y2 => return frst y1
      lazy? y2 => error "last: infinite stream"
      y1 := y2
      y2 := rst y2
      if odd? i then x := rst x
      eq?(x,y2) => error "last: infinite stream"

  if % has FiniteAggregate S then -- # is only defined for finite aggregates
    last(x,n) ==
      possiblyInfinite? x => error "last: infinite stream"
      m := # x
      m < n => error "last: index out of range"
      copy rest(x,(m-n)::NNI)

  elt(x,"last") == last x

  tail x ==
    -- error if stream is not finite
    empty? x => error "tail: empty stream"
    y1 := x
    y2 := rst x
    for i in 0.. repeat
      explicitlyEmpty? y2 => return y1
      lazy? y2 => error "tail: infinite stream"
      y1 := y2
      y2 := rst y2
      if odd? i then x := rst x
      eq?(x,y2) => error "tail: infinite stream"

--% STAGG functions

  possiblyInfinite? x ==
    y := x
    for i in 0.. repeat
      explicitlyEmpty? y  => return false
      lazy? y => return true
      if odd? i then x := rst x
      y := rst y
      eq?(x,y) => return true

  explicitlyFinite? x == not possiblyInfinite? x

--% LZSTAGG functions

  extend(x,n) ==
    y := x
    for i in 1..n while not empty? y repeat y := rst y
    x

  complete x ==
    y := x
    while not empty? y repeat y := rst y
    x

@

\section{package CSTTOOLS CyclicStreamTools}

<<package CSTTOOLS CyclicStreamTools>>=
import Type
import NonNegativeInteger
import LazyStreamAggregate
)abbrev package CSTTOOLS CyclicStreamTools
++ Functions for dealing with cyclic streams
++ Author: Clifton J. Williamson
++ Date Created: 5 December 1989
++ Date Last Updated: 5 December 1989
++ Keywords: stream, cyclic
++ Description:
++ This package provides tools for working with cyclic streams.
CyclicStreamTools(S,ST): Exports == Implementation where
  S  : Type
  ST : LazyStreamAggregate S

  Exports ==> with

    cycleElt: ST -> Union(ST,"failed")
      ++ cycleElt(s) returns a pointer to a node in the cycle if the stream s is
      ++ cyclic and returns "failed" if s is not cyclic
    computeCycleLength: ST -> NonNegativeInteger
      ++ computeCycleLength(s) returns the length of the cycle of a
      ++ cyclic stream t, where s is a pointer to a node in the
      ++ cyclic part of t.
    computeCycleEntry: (ST,ST) -> ST
      ++ computeCycleEntry(x,cycElt), where cycElt is a pointer to a
      ++ node in the cyclic part of the cyclic stream x, returns a
      ++ pointer to the first node in the cycle

  Implementation ==> add

    cycleElt x ==
      y := x
      for i in 0.. repeat
        (explicitlyEmpty? y) or (lazy? y) => return "failed"
        y := rst y
        if odd? i then x := rst x
        eq?(x,y) => return y

    computeCycleLength cycElt ==
      y := cycElt
      for i in 1.. repeat
        y := rst y
        eq?(y,cycElt) => return i

    computeCycleEntry(x,cycElt) ==
      y := rest(x, computeCycleLength cycElt)
      repeat
        eq?(x,y) => return x
        x := rst x ; y := rst y

@
\section{domain STREAM Stream}
<<domain STREAM Stream>>=
import Void
import Boolean
import Integer
import NonNegativeInteger
import UniversalSegment
import List
import OutputForm
)abbrev domain STREAM Stream
++ Implementation of streams via lazy evaluation
++ Authors: Burge, Watt; updated by Clifton J. Williamson
++ Date Created: July 1986
++ Date Last Updated: 30 March 1990
++ Keywords: stream, infinite list, infinite sequence
++ Examples:
++ References:
++ Description:
++ A stream is an implementation of an infinite sequence using
++ a list of terms that have been computed and a function closure
++ to compute additional terms when needed.

Stream(S): Exports == Implementation where
--  problems:
--  1) dealing with functions which basically want a finite structure
--  2) 'map' doesn't deal with cycles very well

  S : Type
  B   ==> Boolean
  OUT ==> OutputForm
  I   ==> Integer
  L   ==> List
  NNI ==> NonNegativeInteger
  U   ==> UniversalSegment I

  Exports == Join(LazyStreamAggregate(S),CoercibleFrom L S,ShallowlyMutableAggregate S) with
    repeating: L S -> %
      ++ repeating(l) is a repeating stream whose period is the list l.
    if S has SetCategory then
      repeating?: (L S,%) -> B
        ++ repeating?(l,s) returns true if a stream s is periodic
        ++ with period l, and false otherwise.
    findCycle: (NNI,%) -> Record(cycle?: B, prefix: NNI, period: NNI)
      ++ findCycle(n,st) determines if st is periodic within n.
    delay: (() -> %) -> %
      ++ delay(f) creates a stream with a lazy evaluation defined by function f.
      ++ Caution: This function can only be called in compiled code.
    cons: (S,%) -> %
      ++ cons(a,s) returns a stream whose \spad{first} is \spad{a}
      ++ and whose \spad{rest} is s.
      ++ Note: \spad{cons(a,s) = concat(a,s)}.
    if S has SetCategory then
      output: (I, %) -> Void
        ++ output(n,st) computes and displays the first n entries
        ++ of st.
      showAllElements: % -> OUT
        ++ showAllElements(s) creates an output form which displays all
        ++ computed elements.
      showAll?: () -> B
        ++ showAll?() returns true if all computed entries of streams
        ++ will be displayed.
        --!! this should be a function of one argument
    setrest!: (%,I,%) -> %
      ++ setrest!(x,n,y) sets rest(x,n) to y. The function will expand
      ++ cycles if necessary.
    generate: (() -> S) -> %
      ++ generate(f) creates an infinite stream all of whose elements are
      ++ equal to \spad{f()}.
      ++ Note: \spad{generate(f) = [f(),f(),f(),...]}.
    generate: (S -> S,S) -> %
      ++ generate(f,x) creates an infinite stream whose first element is
      ++ x and whose nth element (\spad{n > 1}) is f applied to the previous
      ++ element. Note: \spad{generate(f,x) = [x,f(x),f(f(x)),...]}.
    filterWhile: (S -> Boolean,%) -> %
      ++ filterWhile(p,s) returns \spad{[x0,x1,...,x(n-1)]} where
      ++ \spad{s = [x0,x1,x2,..]} and
      ++ n is the smallest index such that \spad{p(xn) = false}.
    filterUntil: (S -> Boolean,%) -> %
      ++ filterUntil(p,s) returns \spad{[x0,x1,...,x(n)]} where
      ++ \spad{s = [x0,x1,x2,..]} and
      ++ n is the smallest index such that \spad{p(xn) = true}.
--    if S has SetCategory then
--      map: ((S,S) -> S,%,%,S) -> %
--       ++ map(f,x,y,a) is equivalent to map(f,x,y)
--       ++ If z = map(f,x,y,a), then z = map(f,x,y) except if
--       ++ x.n = a and rest(rest(x,n)) = rest(x,n) in which case
--       ++ rest(z,n) = rest(y,n) or if y.m = a and rest(rest(y,m)) =
--       ++ rest(y,m) in which case rest(z,n) = rest(x,n).
--       ++ Think of the case where f(xi,yi) = xi + yi and a = 0.

  Implementation ==> add
    MIN ==> 1  -- minimal stream index; see also the defaults in LZSTAGG
    x:%

    import CyclicStreamTools(S,%)

--% representation

    -- The Rep is a pair of one of three kinds:
    --    [value: S,              rest: %]
    --    [%nullStream: Magic,    %nil    ]
    --    [%nonNullStream: Magic, fun: () -> %]
    -- Could use a record of unions if we could guarantee no tags.

    import %nil: %          from Foreign Builtin  -- to indicate nil stream
    import %nullStream: S   from Foreign Builtin  -- end-of-stream token
    import %nonNullStream: S from Foreign Builtin -- plentyfull stream token

    import %head: % -> S     from Foreign Builtin
    import %tail: % -> %     from Foreign Builtin
    import %pair: (S,%) -> % from Foreign Builtin

    explicitlyEmpty? x == %peq(frst x,%nullStream)$Foreign(Builtin)
    lazy? x            == %peq(frst x,%nonNullStream)$Foreign(Builtin)

--% signatures of local functions

    expand!      : (%,I) -> %

--% functions to access or change record fields without lazy evaluation

    frst x == %head x
    rst  x == %tail x

    setfrst!(x: %,s: S): S ==
      %store(%head x,s)$Foreign(Builtin)
      %head x

    setrst!(x:%,y: %): % ==
      %store(%tail x,y)$Foreign(Builtin)
      %tail x

    -- destructively changes x to a null stream
    setToNil!(x: %): % ==
      setfrst!(x,%nullStream)
      setrst!(x,%nil)
      x

--% SETCAT functions

    if S has SetCategory then

      getm              : (%,L OUT,I) -> L OUT
      streamCountCoerce : % -> OUT
      listm             : (%,L OUT,I) -> L OUT

      getm(x,le,n) ==
        explicitlyEmpty? x => le
        lazy? x =>
          positive? n =>
            empty? x => le
            getm(rst x,concat(frst(x) :: OUT,le),n - 1)
          concat(message("..."),le)
        eq?(x,rst x) => concat(overbar(frst(x) :: OUT),le)
        positive? n => getm(rst x,concat(frst(x) :: OUT,le),n - 1)
        concat(message("..."),le)

      streamCountCoerce x ==
      -- this will not necessarily display all stream elements
      -- which have been computed
        count := _$streamCount$Lisp
        -- compute count elements
        y := x
        for i in 1..count while not empty? y repeat y := rst y
        fc := findCycle(count,x)
        not fc.cycle? => bracket reverse! getm(x,empty(),count)
        le : L OUT := empty()
        for i in 1..fc.prefix repeat
          le := concat(first(x) :: OUT,le)
          x := rest x
        pp : OUT :=
          fc.period = 1 => overbar(frst(x) :: OUT)
          pl : L OUT := empty()
          for i in 1..fc.period repeat
            pl := concat(frst(x) :: OUT,pl)
            x  := rest x
          overbar commaSeparate reverse! pl
        bracket reverse! concat(pp,le)

      listm(x,le,n) ==
        explicitlyEmpty? x => le
        lazy? x =>
          positive? n =>
            empty? x => le
            listm(rst x, concat(frst(x) :: OUT,le),n-1)
          concat(message("..."),le)
        listm(rst x,concat(frst(x) :: OUT,le),n-1)

      showAllElements x ==
      -- this will display all stream elements which have been computed
      -- and will display at least n elements with n = streamCount$Lisp
        extend(x,_$streamCount$Lisp)
        cycElt := cycleElt x
        cycElt case "failed" =>
          le := listm(x,empty(),_$streamCount$Lisp)
          bracket reverse! le
        cycEnt := computeCycleEntry(x,cycElt :: %)
        le : L OUT := empty()
        while not eq?(x,cycEnt) repeat
          le := concat(frst(x) :: OUT,le)
          x := rst x
        len := computeCycleLength(cycElt :: %)
        pp : OUT :=
          len = 1 => overbar(frst(x) :: OUT)
          pl : L OUT := []
          for i in 1..len repeat
            pl := concat(frst(x) :: OUT,pl)
            x := rst x
          overbar commaSeparate reverse! pl
        bracket reverse! concat(pp,le)

      showAll?() ==
        NULL(_$streamsShowAll$Lisp)$Lisp => false
        true

      coerce(x):OUT ==
        showAll?() => showAllElements x
        streamCountCoerce x

--% AGG functions

    lazyCopy:% -> %
    lazyCopy x == delay
      empty? x => empty()
      concat(frst x, copy rst x)

    copy x ==
      cycElt := cycleElt x
      cycElt case "failed" => lazyCopy x
      ce := cycElt :: %
      len := computeCycleLength(ce)
      e := computeCycleEntry(x,ce)
      d := distance(x,e)
      cycle := complete first(e,len)
      setrst!(tail cycle,cycle)
      d = 0 => cycle
      head := complete first(x,d::NNI)
      setrst!(tail head,cycle)
      head

--% CNAGG functions

    construct l ==
      -- copied from defaults to avoid loading defaults
      empty? l => empty()
      concat(first l, construct rest l)

--% ELTAGG functions

    elt(x:%,n:I) ==
      -- copied from defaults to avoid loading defaults
      n < MIN or empty? x => error "elt: no such element"
      n = MIN => frst x
      elt(rst x,n - 1)

    seteltt:(%,I,S) -> S
    seteltt(x,n,s) ==
      n = MIN => setfrst!(x,s)
      seteltt(rst x,n - 1,s)

    setelt(x,n:I,s:S) ==
      n < MIN or empty? x => error "setelt: no such element"
      x := expand!(x,n - MIN + 1)
      seteltt(x,n,s)

--% IXAGG functions

    removee: ((S -> Boolean),%) -> %
    removee(p,x) == delay
      empty? x => empty()
      p(frst x) => remove(p,rst x)
      concat(frst x,remove(p,rst x))

    remove(p: S -> Boolean,x:%) ==
      explicitlyEmpty? x => empty()
      eq?(x,rst x) =>
        p(frst x) => empty()
        x
      removee(p,x)

    selectt: ((S -> Boolean),%) -> %
    selectt(p,x) == delay
      empty? x => empty()
      not p(frst x) => select(p, rst x)
      concat(frst x,select(p,rst x))

    select(p,x) ==
      explicitlyEmpty? x => empty()
      eq?(x,rst x) =>
        p(frst x) => x
        empty()
      selectt(p,x)

    map(f,x) ==
      map(f,x pretend Stream(S))$StreamFunctions2(S,S) pretend %

    map(g,x,y) ==
      xs := x pretend Stream(S); ys := y pretend Stream(S)
      map(g,xs,ys)$StreamFunctions3(S,S,S) pretend %

    fill!(x,s) ==
      setfrst!(x,s)
      setrst!(x,x)

    map!(f,x) ==
    -- too many problems with map! on a lazy stream, so
    -- in this case, an error message is returned
      cyclic? x =>
        tail := cycleTail x ; y := x
        until y = tail repeat
          setfrst!(y,f frst y)
          y := rst y
        x
      explicitlyFinite? x =>
        y := x
        while not empty? y repeat
          setfrst!(y,f frst y)
          y := rst y
        x
      error "map!: stream with lazy evaluation"

    swap!(x,m,n) ==
      (not index?(m,x)) or (not index?(n,x)) =>
        error "swap!: no such elements"
      x := expand!(x,max(m,n) - MIN + 1)
      xm := elt(x,m); xn := elt(x,n)
      setelt(x,m,xn); setelt(x,n,xm)
      x

--% LNAGG functions

    concat(x:%,s:S) == delay
      empty? x => concat(s,empty())
      concat(frst x,concat(rst x,s))

    concat(x:%,y:%) == delay
      empty? x => y
      concat(frst x,concat(rst x, y))

    concat l == delay
      empty? l => empty()
      empty?(x := first l) => concat rest l
      concat(frst x,concat(rst x,concat rest l))

    setelt(x,seg:U,s:S) ==
      low := lo seg
      hasHi seg =>
        high := hi seg
        high < low => s
        (not index?(low,x)) or (not index?(high,x)) =>
          error "setelt: index out of range"
        x := expand!(x,high - MIN + 1)
        y := rest(x,(low - MIN) :: NNI)
        for i in 0..(high-low) repeat
          setfrst!(y,s)
          y := rst y
        s
      not index?(low,x) => error "setelt: index out of range"
      x := rest(x,(low - MIN) :: NNI)
      setrst!(x,x)
      setfrst!(x,s)

--% RCAGG functions

    empty() ==
      %pair(%nullStream,%nil)

    lazyEval(x: %): % ==
      (rst(x):(()-> %)) ()

    lazyEvaluate x ==
      st := lazyEval x
      setfrst!(x, frst st)
      setrst!(x,if %peq(rst st,st)$Foreign(Builtin) then x else rst st)
      x

    -- empty? is the only function that explicitly causes evaluation
    -- of a stream element
    empty? x ==
      while lazy? x repeat
        st := lazyEval x
        setfrst!(x, frst st)
        setrst!(x,if %peq(rst st,st)$Foreign(Builtin) then x else rst st)
      explicitlyEmpty? x

    --setvalue(x,s) == setfirst!(x,s)

    --setchildren(x,l) ==
      --empty? l => error "setchildren: empty list of children"
      --not(empty? rest l) => error "setchildren: wrong number of children"
      --setrest!(x,first l)

--% URAGG functions

    first(x,n) == delay
    -- former name: take
      n = 0 or empty? x => empty()
      (concat(frst x, first(rst x,(n-1) :: NNI)))

    concat(s:S,x:%) ==
      %pair(s,x)

    cons(s,x) == concat(s,x)

    cycleSplit! x ==
      cycElt := cycleElt x
      cycElt case "failed" =>
        error "cycleSplit!: non-cyclic stream"
      y := computeCycleEntry(x,cycElt :: %)
      eq?(x,y) => (setToNil! x; return y)
      z := rst x
      repeat
        eq?(y,z) => (setrest!(x,empty()); return y)
        x := z ; z := rst z

    expand!(x,n) ==
    -- expands cycles (if necessary) so that the first n
    -- elements of x will not be part of a cycle
      n < 1 => x
      y := x
      for i in 1..n while not empty? y repeat y := rst y
      cycElt := cycleElt x
      cycElt case "failed" => x
      e := computeCycleEntry(x,cycElt :: %)
      d : I := distance(x,e)
      d >= n => x
      if d = 0 then
        -- roll the cycle 1 entry
        d := 1
        t := cycleTail e
        if eq?(t,e) then
          t := concat(frst t,empty())
          e := setrst!(t,t)
          setrst!(x,e)
        else
          setrst!(t,concat(frst e,rst e))
          e := rst e
      nLessD := (n-d) :: NNI
      y := complete first(e,nLessD)
      e := rest(e,nLessD)
      setrst!(tail y,e)
      setrst!(rest(x,(d-1) :: NNI),y)
      x

    first x ==
      empty? x => error "Can't take the first of an empty stream."
      frst x

    concat!(x:%,y:%) ==
      empty? x => y
      setrst!(tail x,y)

    concat!(x:%,s:S) ==
      concat!(x,concat(s,empty()))

    setfirst!(x,s) == setelt(x,0,s)
    setelt(x,"first",s) == setfirst!(x,s)
    setrest!(x,y) ==
      empty? x => error "setrest!: empty stream"
      setrst!(x,y)
    setelt(x,"rest",y) == setrest!(x,y)

    setlast!(x,s) ==
      empty? x => error "setlast!: empty stream"
      setfrst!(tail x, s)
    setelt(x,"last",s) == setlast!(x,s)

    split!(x,n) ==
      n < MIN => error "split!: index out of range"
      n = MIN =>
        y : % := empty()
        setfrst!(y,frst x)
        setrst!(y,rst x)
        setToNil! x
        y
      x := expand!(x,n - MIN)
      x := rest(x,(n - MIN - 1) :: NNI)
      y := rest x
      setrst!(x,empty())
      y

--% STREAM functions

    coerce(l: L S) == construct l

    repeating l ==
      empty? l =>
        error "Need a non-null list to make a repeating stream."
      x0 : % := x := construct l
      while not empty? rst x repeat x := rst x
      setrst!(x,x0)

    if S has SetCategory then

      repeating?(l, x) ==
        empty? l =>
          error "Need a non-empty? list to make a repeating stream."
        empty? rest l =>
          not empty? x and frst x = first l and x = rst x
        x0 := x
        for s in l repeat
          empty? x or s ~= frst x => return false
          x := rst x
        eq?(x,x0)

    findCycle(n, x) ==
      hd := x
      -- Determine whether periodic within n.
      tl := rest(x, n)
      explicitlyEmpty? tl => [false, 0, 0]
      i := 0; while not eq?(x,tl) repeat (x := rst x; i := i + 1)
      i = n => [false, 0, 0]
      -- Find period. Now x=tl, so step over and find it again.
      x := rst x; periode := 1
      while not eq?(x,tl) repeat (x := rst x; periode := periode + 1)
      -- Find non-periodic part.
      x := hd; xp := rest(hd, periode); npp := 0
      while not eq?(x,xp) repeat (x := rst x; xp := rst xp; npp := npp+1)
      [true, npp, periode]

    delay(fs:()->%) ==
      %pair(%nonNullStream,fs : %)

    explicitEntries? x ==
      not explicitlyEmpty? x and not lazy? x

    numberOfComputedEntries x ==
      explicitEntries? x => numberOfComputedEntries(rst x) + 1
      0

    if S has SetCategory then

      output(n,x) ==
        (not(positive? n)) or empty? x => void()
        mathPrint(frst(x)::OUT)$Lisp
        output(n-1, rst x)

    setrestt!(x: %,n: I,y: %): % ==
      n = 0 => setrst!(x,y)
      setrestt!(rst x,n-1,y)

    setrest!(x,n,y) ==
      negative? n or empty? x => error "setrest!: no such rest"
      x := expand!(x,n+1)
      setrestt!(x,n,y)

    generate f    == delay concat(f(), generate f)
    gen:(S -> S,S) -> %
    gen(f,s) == delay(ss:=f s; concat(ss, gen(f,ss)))
    generate(f,s)==concat(s,gen(f,s))

    swhilee:(S -> Boolean,%) -> %
    swhilee(p,x) == delay
      empty? x      => empty()
      not p(frst x) => empty()
      concat(frst x,filterWhile(p,rst x))
    filterWhile(p,x)==
      explicitlyEmpty? x => empty()
      eq?(x,rst x) =>
        p(frst x) => x
        empty()
      swhilee(p,x)

    suntill: (S -> Boolean,%) -> %
    suntill(p,x) == delay
      empty? x  => empty()
      p(frst x) => concat(frst x,empty())
      concat(frst x, filterUntil(p, rst x))

    filterUntil(p,x)==
      explicitlyEmpty? x => empty()
      eq?(x,rst x) =>
        p(frst x) => concat(frst x,empty())
        x
      suntill(p,x)

--  if S has SetCategory then
--    mapp: ((S,S) -> S,%,%,S) -> %
--    mapp(f,x,y,a) == delay
--      empty? x or empty? y => empty()
--      concat(f(frst x,frst y), map(f,rst x,rst y,a))
--      map(f,x,y,a) ==
--      explicitlyEmpty? x => empty()
--      eq?(x,rst x) =>
--        frst x=a => y
--        map(f(frst x,#1),y)
--      explicitlyEmpty? y => empty()
--      eq?(y,rst y) =>
--        frst y=a => x
--        p(f(#1,frst y),x)
--      mapp(f,x,y,a)

@

\section{package STREAM1 StreamFunctions1}

<<package STREAM1 StreamFunctions1>>=
import Type
import Stream
)abbrev package STREAM1 StreamFunctions1
++ Authors: Burge, Watt; updated by Clifton J. Williamson
++ Date Created: July 1986
++ Date Last Updated: 29 January 1990
++ Keywords: stream, infinite list, infinite sequence
StreamFunctions1(S:Type): Exports == Implementation where
  ++ Functions defined on streams with entries in one set.
  ST  ==> Stream

  Exports ==> with
    concat: ST ST S -> ST S
      ++ concat(u) returns the left-to-right concatentation of the streams in u.
      ++ Note: \spad{concat(u) = reduce(concat,u)}.

  Implementation ==> add

    concat z == delay
      empty? z => empty()
      empty?(x := frst z) => concat rst z
      concat(frst x,concat(rst x,concat rst z))

@

\section{package STREAM2 StreamFunctions2}

<<package STREAM2 StreamFunctions2>>=
import Type
import Stream
)abbrev package STREAM2 StreamFunctions2
++ Authors: Burge, Watt; updated by Clifton J. Williamson
++ Date Created: July 1986
++ Date Last Updated: 29 January 1990
++ Keywords: stream, infinite list, infinite sequence
StreamFunctions2(A:Type,B:Type): Exports == Implementation where
  ++ Functions defined on streams with entries in two sets.
  ST   ==> Stream

  Exports ==> with
    map: ((A -> B),ST A) -> ST B
      ++ map(f,s) returns a stream whose elements are the function f applied
      ++ to the corresponding elements of s.
      ++ Note: \spad{map(f,[x0,x1,x2,...]) = [f(x0),f(x1),f(x2),..]}.
    scan: (B,((A,B) -> B),ST A) -> ST B
      ++ scan(b,h,[x0,x1,x2,...]) returns \spad{[y0,y1,y2,...]}, where
      ++ \spad{y0 = h(x0,b)},
      ++ \spad{y1 = h(x1,y0)},\spad{...}
      ++ \spad{yn = h(xn,y(n-1))}.
    reduce:  (B,(A,B) -> B,ST A) -> B
      ++ reduce(b,f,u), where u is a finite stream \spad{[x0,x1,...,xn]},
      ++ returns the value \spad{r(n)} computed as follows:
      ++ \spad{r0 = f(x0,b),
      ++ r1 = f(x1,r0),...,
      ++ r(n) = f(xn,r(n-1))}.
--  rreduce: (B,(A,B) -> B,ST A) -> B
--    ++ reduce(b,h,[x0,x1,..,xn]) = h(x1,h(x2(..,h(x(n-1),h(xn,b))..)
--  reshape: (ST B,ST A) -> ST B
--    ++ reshape(y,x) = y

  Implementation ==> add

    mapp: (A -> B,ST A) -> ST B
    mapp(f,x)== delay
      empty? x => empty()
      concat(f frst x, map(f,rst x))

    map(f,x) ==
      explicitlyEmpty? x => empty()
      eq?(x,rst x) => repeating([f frst x])
      mapp(f, x)

--  reshape(y,x) == y

    scan(b,h,x) == delay
      empty? x => empty()
      c := h(frst x,b)
      concat(c,scan(c,h,rst x))

    reduce(b,h,x) ==
      empty? x => b
      reduce(h(frst x,b),h,rst x)
--  rreduce(b,h,x) ==
--    empty? x => b
--    h(frst x,rreduce(b,h,rst x))

@

\section{package STREAM3 StreamFunctions3}

<<package STREAM3 StreamFunctions3>>=
import Type
import Stream
)abbrev package STREAM3 StreamFunctions3
++ Authors: Burge, Watt; updated by Clifton J. Williamson
++ Date Created: July 1986
++ Date Last Updated: 29 January 1990
++ Keywords: stream, infinite list, infinite sequence
StreamFunctions3(A,B,C): Exports == Implementation where
  ++ Functions defined on streams with entries in three sets.
  A  : Type
  B  : Type
  C  : Type
  ST ==> Stream

  Exports ==> with
    map: ((A,B) -> C,ST A,ST B) -> ST C
      ++ map(f,st1,st2) returns the stream whose elements are the
      ++ function f applied to the corresponding elements of st1 and st2.
      ++ Note: \spad{map(f,[x0,x1,x2,..],[y0,y1,y2,..]) = [f(x0,y0),f(x1,y1),..]}.

  Implementation ==> add

    mapp:((A,B) -> C,ST A,ST B) -> ST C
    mapp(g,x,y) == delay
      empty? x or empty? y => empty()
      concat(g(frst x,frst y), map(g,rst x,rst y))

    map(g,x,y) ==
      explicitlyEmpty? x => empty()
      eq?(x,rst x) => map(g(frst x,#1),y)$StreamFunctions2(B,C)
      explicitlyEmpty? y => empty()
      eq?(y,rst y) => map(g(#1,frst y),x)$StreamFunctions2(A,C)
      mapp(g,x,y)

@
\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>>

<<category LZSTAGG LazyStreamAggregate>>
<<package CSTTOOLS CyclicStreamTools>>
<<domain STREAM Stream>>
<<package STREAM1 StreamFunctions1>>
<<package STREAM2 StreamFunctions2>>
<<package STREAM3 StreamFunctions3>>
@
\eject
\begin{thebibliography}{99}
\bibitem{1} nothing
\end{thebibliography}
\end{document}