71 lines
1.9 KiB
Dart
71 lines
1.9 KiB
Dart
import 'dart:math';
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import 'dart:io';
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import 'package:angel3_combinator/angel3_combinator.dart';
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import 'package:string_scanner/string_scanner.dart';
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/// Note: This grammar does not handle precedence, for the sake of simplicity.
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Parser<num> calculatorGrammar() {
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var expr = reference<num>();
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var number = match<num>(RegExp(r'-?[0-9]+(\.[0-9]+)?'))
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.value((r) => num.parse(r.span!.text));
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var hex = match<int>(RegExp(r'0x([A-Fa-f0-9]+)'))
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.map((r) => int.parse(r.scanner.lastMatch![1]!, radix: 16));
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var binary = match<int>(RegExp(r'([0-1]+)b'))
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.map((r) => int.parse(r.scanner.lastMatch![1]!, radix: 2));
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var alternatives = <Parser<num>>[];
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void registerBinary(String op, num Function(num, num) f) {
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alternatives.add(
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chain<num>([
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expr.space(),
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match<Null>(op).space() as Parser<num>,
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expr.space(),
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]).map((r) => f(r.value![0], r.value![2])),
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);
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}
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registerBinary('**', (a, b) => pow(a, b));
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registerBinary('*', (a, b) => a * b);
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registerBinary('/', (a, b) => a / b);
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registerBinary('%', (a, b) => a % b);
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registerBinary('+', (a, b) => a + b);
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registerBinary('-', (a, b) => a - b);
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registerBinary('^', (a, b) => a.toInt() ^ b.toInt());
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registerBinary('&', (a, b) => a.toInt() & b.toInt());
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registerBinary('|', (a, b) => a.toInt() | b.toInt());
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alternatives.addAll([
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number,
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hex,
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binary,
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expr.parenthesized(),
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]);
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expr.parser = longest(alternatives);
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return expr;
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}
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void main() {
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var calculator = calculatorGrammar();
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while (true) {
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stdout.write('Enter an expression: ');
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var line = stdin.readLineSync()!;
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var scanner = SpanScanner(line, sourceUrl: 'stdin');
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var result = calculator.parse(scanner);
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if (!result.successful) {
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for (var error in result.errors) {
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stderr.writeln(error.toolString);
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stderr.writeln(error.span!.highlight(color: true));
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}
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} else {
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print(result.value);
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}
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}
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}
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