forked from KolibriOS/kolibrios
123 lines
2.5 KiB
Plaintext
123 lines
2.5 KiB
Plaintext
(*
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adapted to Oberon-07 by 0CodErr, KolibriOS team
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*)
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(* Example program from Programming In Modula-2, N. Wirth., pg. 56, *)
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(* - no WINDOWS in this example *)
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(* this program translates a small language into postfix form
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* the language is
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*
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* expression = term { [ "+" | "-" ] term }
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*
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* term = factor { [ "*" | "/" ] factor }
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*
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* factor = letter | "(" expression ")"
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*
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* letter = "a" | 'b" | … | "z"
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*
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* try as input
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* a+b
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* a*b+c
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* a+b*c
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* a*(b/(c-d))
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*)
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MODULE postfix;
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IMPORT In, Out, Console;
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CONST
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OUT_LINE_SIZE = 80;
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IN_LINE_SIZE = 80;
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VAR
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ch : CHAR;
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i, index : INTEGER;
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out_line : ARRAY OUT_LINE_SIZE OF CHAR;
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in_line : ARRAY IN_LINE_SIZE OF CHAR;
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cur_ch : INTEGER;
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PROCEDURE NextChar(): CHAR;
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BEGIN
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INC(cur_ch)
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RETURN in_line[cur_ch - 1]
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END NextChar;
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PROCEDURE expression;
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VAR
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addop :CHAR;
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PROCEDURE term;
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VAR
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mulop :CHAR;
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PROCEDURE factor;
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BEGIN (* factor *)
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IF ch = "(" THEN
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ch := NextChar();
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expression;
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WHILE ch # ")" DO
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ch := NextChar()
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END (* WHILE *)
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ELSE
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WHILE (ch < "a") OR (ch > "z") DO
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ch := NextChar()
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END; (* WHILE *)
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out_line[index] := ch;
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index := index + 1
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END; (* IF *)
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ch := NextChar()
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END factor;
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BEGIN (* term *)
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factor;
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WHILE (ch = "*") OR (ch = "/") DO
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mulop := ch;
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ch := NextChar();
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factor;
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out_line[index] := mulop;
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index := index + 1
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END (* WHILE *)
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END term;
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BEGIN (* expression *)
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term;
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WHILE (ch = "+") OR (ch = "-") DO
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addop := ch;
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ch := NextChar();
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term;
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out_line[index] := addop;
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index := index + 1
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END (* WHILE *)
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END expression;
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BEGIN (* Postfix *)
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Console.open;
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index := 1; cur_ch := 0;
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Out.String("Enter expression:");
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In.String(in_line);
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ch := NextChar();
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WHILE ch > " " DO
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expression;
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FOR i := 1 TO index - 1 DO
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Out.Char(out_line[i])
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END; (* FOR *)
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Out.Ln;
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index := 1; cur_ch := 0;
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Out.String("Enter expression:");
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In.String(in_line);
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ch := NextChar()
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END; (* WHILE *)
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Console.exit(TRUE)
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END postfix. |