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Arithmetic evaluation: Difference between revisions
→{{header|Prolog}}: works with swipl + lang tag
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=={{header|Prolog}}==
{{works with|SWI Prolog}}
<lang prolog> % Lexer
numeric(X) :- 48 =< X, X =< 57.
not_numeric(X) :- 48 > X ; X > 57.
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lex2([Xa,Xb|Xs], [Xa|Ys]) :- number(Xa), atom(Xb), lex2([Xb|Xs], Ys).
lex2([Xa,Xb|Xs], [Y|Ys]) :- number(Xa), number(Xb), N is Xa * 10 + Xb, lex2([N|Xs], [Y|Ys]).
% Parser
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% Example use
% calculator("(3+50)*7-9", X).</lang>
=={{header|Python}}==
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