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Ingy döt Net 2023-07-01 11:58:00 -04:00
parent 72d218235f
commit f23f22d71c
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Task/Arithmetic-evaluation/XPL0/arithmetic-evaluation.xpl0 Normal file
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def \Node\ Left, Data, Right;
def IntSize = 4;
int Stack(16);
int SP; \stack pointer
proc Push(N);
int N;
[Stack(SP):= N; SP:= SP+1];
func Pop;
[SP:= SP-1; return Stack(SP)];
func Precedence(Op);
int Op;
case Op of
^+, ^-: return 2;
^*, ^/: return 3;
^^: return 4
other [];
proc PostOrder(Node); \Traverse tree at Node in postorder, and
int Node, Top; \ return its evaluation on the stack
[if Node # 0 then
[PostOrder(Node(Left));
PostOrder(Node(Right));
case Node(Data) of
^+: [Top:= Pop; Push(Pop+Top)];
^-: [Top:= Pop; Push(Pop-Top)];
^*: [Top:= Pop; Push(Pop*Top)];
^/: [Top:= Pop; Push(Pop/Top)]
other Push(Node(Data) - ^0); \convert ASCII to binary
];
];
char Str;
int Token, Op1, Op2, Node;
[Str:= "3 + 4 * 2 / ( 1 - 5 ) "; \RPN: 342*15-/+
Text(0, Str);
\Convert infix expression to RPN (postfix) using shunting-yard algorithm
SP:= 0;
OpenO(8); \discard (overwrite) arguments in RPi's command line
loop [repeat Token:= Str(0); Str:= Str+1;
until Token # ^ ; \strip out space characters
case Token of
^+, ^-, ^*, ^/, ^^:
[Op1:= Token;
loop [if SP <= 0 then quit; \stack is empty
Op2:= Stack(SP-1);
if Op2 = ^( then quit;
if Precedence(Op2) < Precedence(Op1) then quit;
if Precedence(Op2) = Precedence(Op1) then
if Op1 = ^^ then quit;
ChOut(8, Pop);
];
Push(Op1);
];
^(: Push(Token);
^): [while SP > 0 and Stack(SP-1) # ^( do
ChOut(8, Pop);
Pop; \discard left parenthesis
];
$A0: quit \terminating space with its MSB set
other ChOut(8, Token); \output the single-digit number
];
while SP > 0 do ChOut(8, Pop); \output any remaining operators
\Build AST from RPN expression
OpenI(8); \(for safety)
loop [Token:= ChIn(8);
if Token = $1A\EOF\ then quit
else if Token >= ^0 and Token <= ^9 then
[Node:= Reserve(3*IntSize);
Node(Data):= Token;
Node(Left):= 0;
Node(Right):= 0;
Push(Node);
]
else \must be an operator
[Node:= Reserve(3*IntSize);
Node(Data):= Token;
Node(Right):= Pop;
Node(Left):= Pop;
Push(Node);
];
];
\Evaluate expression in AST
PostOrder(Pop);
Text(0, "= ");
IntOut(0, Pop);
]