
/* See the documentation on the assignment of the precedence of the rules.
 */

/* Some very basic functions that are used always any way... */


/* Implementation of Nth that allows extending. */
RuleBase("Nth",{alist,aindex});
Rule("Nth",2,10,
    And(Equals(IsFunction(alist),True),
            Equals(IsInteger(aindex),True),
            Not(Equals(Head(Listify(alist)),Nth))
            ))
     MathNth(alist,aindex);




Rule("Nth",2,14,
     And(Equals(IsString(alist),True),IsList(aindex))
    )
[
  Local(result);
  result:="";
  ForEach(i,aindex) [ result := result : StringMid'Get(i,1,alist); ];
  result;
];

Rule("Nth",2,15,Equals(IsString(alist),True))
[
  StringMid'Get(aindex,1,alist);
];


Rule("Nth",2,20,Equals(IsList(aindex),True))
[
  Map({{ii},alist[ii]},{aindex});
];

Rule("Nth",2,30,
   And(
           Equals(IsGeneric(alist),True),
           Equals(GenericTypeName(alist),"Array"),
           Equals(IsInteger(aindex),True)
          )
    )
[
  Array'Get(alist,aindex);
];



Rule("Nth",2,40,Equals(IsString(aindex),True))
[
  Local(as);
  as := Assoc(aindex,alist);
  If (Not(Equals(as,Empty)),Set(as,Nth(as,2)));
  as;
];

Protect(Nth);

Function("NrArgs",{aLeft}) Length(Listify(aLeft))-1;

10 # IsNonObject(Object(_x)) <-- False;
20 # IsNonObject(_x)         <-- True;

1 # Numer(_x / _y)      <-- x;
2 # Numer(x_IsNumber)   <-- x;
1 # Denom(_x / _y)      <-- y;
2 # Denom(x_IsNumber)   <-- 1;

/* Implementation of numeric mode */
LocalSymbols(Numeric) [
  Set(Numeric,False);

  // evaluate numerically with given precision
  LocalSymbols(prev'Numeric, prev'digits, numeric'result) Macro("N",{expr,digits})
  [ // we were in non-numeric mode
      Local(prev'Numeric, prev'digits, numeric'result,errorString);
      Set(prev'digits, Builtin'Precision'Get());
      Builtin'Precision'Set(@digits);
      AssignCachedConstantsN();
      Set(prev'Numeric,Numeric);
      Set(Numeric, True);
      Set(errorString,"");
      TrapError(Set(numeric'result, @expr),Set(errorString,GetCoreError()));
      Set(Numeric,prev'Numeric);
      If(Not Numeric,[
          // clear constants
          ClearCachedConstantsN();
      ]);
      Builtin'Precision'Set(prev'digits);
      Check(errorString="",errorString);
      numeric'result;
  ];

  LocalSymbols(dig,ex) Macro("N",{expr})
  [
    Local(dig,ex);
    Set(dig,Builtin'Precision'Get());
    Set(ex,Hold(@expr));
    `N(@ex,@dig);
  ];

  LocalSymbols(result) Macro("NonN",{expr})
  [
    Local(result);
    GlobalPush(Numeric);
    Numeric := False;
    result := (@expr);
    Numeric := GlobalPop();
    result;
  ];

  Function("InNumericMode",{}) Numeric;

]; //LocalSymbols(Numeric)

LocalSymbols(Verbose) [
  Set(Verbose,False);
  Function("V",{aNumberBody})
  [
    Local(prevVerbose,result);
    Set(prevVerbose,Verbose);
    Set(Verbose,True);
    Set(result,Eval(aNumberBody));
    Set(Verbose,prevVerbose);
    result;
  ];
  Function("InVerboseMode",{}) Verbose;

]; // LocalSymbols(Verbose)
HoldArg("V",aNumberBody);
UnFence("V",1);

Function("++",{aVar})
[
   MacroSet(aVar,MathAdd(Eval(aVar),1));
];
UnFence("++",1);
HoldArg("++",aVar);


Function("--",{aVar})
[
   MacroSet(aVar,MathSubtract(Eval(aVar),1));
];
UnFence("--",1);
HoldArg("--",aVar);


Function("TableForm",{list})
[
  Local(i);
  ForEach(i,list)
  [
    Write(i);
    NewLine();
  ];
  True;
];

RuleBase("NormalForm",{expression});
Rule("NormalForm",1,1000,True) expression;




RuleBase("==",{left,right});
RuleBase("!==",{left,right});

UnProtect(%);

a_IsNonNegativeInteger & b_IsNonNegativeInteger <-- BitAnd(a,b);
a_IsNonNegativeInteger | b_IsNonNegativeInteger <-- BitOr(a,b);
a_IsNonNegativeInteger % b_IsPositiveInteger <-- Mod(a,b);

Protect(%);

RuleBase("if",{predicate,body});
(if(True) _body) <-- Eval(body);
HoldArg("if",body);
UnFence("if",2);

RuleBase("else",{ifthen,otherwise});
0 # (if (_predicate) _body else _otherwise)_(Eval(predicate) = True) <--
     Eval(body);
0 # (if (_predicate) _body else _otherwise)_(Eval(predicate) = False) <--
     Eval(otherwise);
1 # (if (_predicate) _body else _otherwise) <--
    UnList({Atom("else"),
            UnList({Atom("if"), (Eval(predicate)), body}),
            otherwise});
HoldArg("else",ifthen);
HoldArg("else",otherwise);
UnFence("else",2);

