path: root/src/boot/utility.boot

-- Copyright (C) 2011, Gabriel Dos Reis.
-- 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
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--%
--% Definitions in this file provide runtime support for the Boot
--% language.  As such, some of the definitions (e.g. reverse, append, etc)
--% use `unusual' style.  These functions are used in code generated
--% by the Boot translator.  Others are handy library functions.
--%

import initial_-env
namespace BOOTTRAN

module utility (objectMember?, symbolMember?, stringMember?,
  charMember?, scalarMember?, listMember?, reverse, reverse!,
  lastNode, append, append!, copyList, substitute, substitute!,
  setDifference, applySubst, applySubst!, applySubstNQ,
  remove,removeSymbol,atomic?,finishLine) where
    substitute: (%Thing,%Thing,%Thing) -> %Thing
    substitute!: (%Thing,%Thing,%Thing) -> %Thing
    append: (%List %Thing,%List %Thing) -> %List %Thing
    append!: (%List %Thing,%List %Thing) -> %List %Thing
    copyList: %List %Thing -> %List %Thing
    lastNode: %List %Thing -> %Maybe %Node %Thing
    removeSymbol: (%List %Thing, %Symbol) -> %List %Thing
    remove: (%List %Thing, %Thing) -> %List %Thing
    atomic?: %Thing -> %Boolean
    finishLine: %Thing -> %Void

--%

++ Return true if `x' is an atom of a quotation.
atomic? x ==
  x isnt [.,:.] or x.op is 'QUOTE

--% membership operators

objectMember?(x,l) ==
  repeat
    l = nil => return false
    cons? l =>
      sameObject?(x,first l) => return true
      l := rest l
    return sameObject?(x,l)

symbolMember?(s,l) ==
  repeat
    l = nil => return false
    cons? l =>
      symbolEq?(s,first l) => return true
      l := rest l
    return symbolEq?(s,l)

stringMember?(s,l) ==
  repeat
    l = nil => return false
    cons? l =>
      stringEq?(s,first l) => return true
      l := rest l
    return stringEq?(s,l)

charMember?(c,l) ==
  repeat
    l = nil => return false
    cons? l =>
      charEq?(c,first l) => return true
      l := rest l
    return charEq?(c,l)

scalarMember?(s,l) ==
  repeat
    l = nil => return false
    cons? l =>
      scalarEq?(s,first l) => return true
      l := rest l
    return scalarEq?(s,l)

listMember?(x,l) ==
  repeat
    l = nil => return false
    cons? l =>
      listEq?(x,first l) => return true
      l := rest l
    return listEq?(x,l)

--% list reversal

reverse l ==
  r := nil
  repeat
    cons? l =>
      r := [first l,:r]
      l := rest l
    return r

reverse! l ==
  l1 := nil
  repeat
    cons? l =>
      l2 := rest l
      l.rest := l1
      l1 := l
      l := l2
    return l1
    
--% return a pointer to the last cons-cell in the list `l'.

lastNode l ==
  while l is [.,:l'] and cons? l' repeat
    l := l'
  l

--% list copying
copyList l ==
  not cons? l => l
  l' := t := [first l]
  repeat
    l := rest l
    cons? l =>
      t.rest := [first l]
      t := rest t
    t.rest := l
    return l'

--% append

append!(x,y) ==
  x = nil => y
  y = nil => x
  lastNode(x).rest := y
  x

append(x,y) ==
  append!(copyList x,y)

--% a-list

assocSymbol(s,al) ==
  repeat
    al is [x,:al] =>
      cons? x and symbolEq?(s,first x) =>
        return x
    return nil

--% substitution

substitute!(y,x,s) ==
  s = nil => nil
  sameObject?(x,s) => y
  if cons? s then
    s.first := substitute!(y,x,first s)
    s.rest := substitute!(y,x,rest s)
  s

substitute(y,x,s) ==
  s = nil => nil
  sameObject?(x,s) => y
  cons? s =>
    h := substitute(y,x,first s)
    t := substitute(y,x,rest s)
    sameObject?(h,first s) and sameObject?(t,rest s) => s
    [h,:t]
  s
  
applySubst(sl,t) ==
  cons? t =>
    hd := applySubst(sl,first t)
    tl := applySubst(sl,rest t)
    sameObject?(hd,first t) and sameObject?(tl,rest t) => t
    [hd,:tl]
  symbol? t and (p := assocSymbol(t,sl)) => rest p
  t

applySubst!(sl,t) ==
  cons? t =>
    hd := applySubst!(sl,first t)
    tl := applySubst!(sl,rest t)
    t.first := hd
    t.rest := tl
  symbol? t and (p := assocSymbol(t,sl)) => rest p
  t

++ Like applySubst, but skip quoted materials.
applySubstNQ(sl,t) ==
  t is [hd,:tl] =>
    hd is "QUOTE" => t
    hd := applySubstNQ(sl,hd)
    tl := applySubstNQ(sl,tl)
    sameObject?(hd,first t) and sameObject?(tl,rest t) => t
    [hd,:tl]
  symbol? t and (p := assocSymbol(t,sl)) => rest p
  t

--% set operations

setDifference(x,y) ==
  x = nil => nil
  y = nil => x
  l := p := [nil]
  for [a,:.] in tails x | not objectMember?(a,y) repeat
    p.rest := [a]
    p := rest p
  rest l

--% removal

removeSymbol(l,x) ==
  before := nil
  l' := l
  repeat
    not cons? l' => return l
    [y,:l'] := l'
    symbolEq?(x,y) => return append!(reverse! before,l')
    before := [y,:before]

removeScalar(l,x) ==
  before := nil
  l' := l
  repeat
    not cons? l' => return l
    [y,:l'] := l'
    scalarEq?(x,y) => return append!(reverse! before,l')
    before := [y,:before]

removeValue(l,x) ==
  before := nil
  l' := l
  repeat
    not cons? l' => return l
    [y,:l'] := l'
    valueEq?(x,y) => return append!(reverse! before,l')
    before := [y,:before]

remove(l,x) ==
  symbol? x => removeSymbol(l,x)
  char? x or integer? x => removeScalar(l,x)
  removeValue(l,x)

--% search

++ Return the index of the character `c' in the string `s', if present.
++ Otherwise, return nil.
charPosition(c,s,k) ==
  n := # s
  repeat
    k >= n => return nil
    stringChar(s,k) = c => return k
    k := k + 1

--% I/O

++ Add a newline character and flush the output stream.
finishLine out ==
  writeNewline out
  flushOutput out