Fix: Operator precedence is not respected #75
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antlr-kotlin-runtime/src/commonTest/kotlin/MiniCalcParserTest.kt
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tianyu
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Actually, I'm having trouble parsing expressions like
It makes a big difference! |
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| @test | ||
| fun testOperatorPrecedence() { | ||
| val input = CharStreams.fromString("1 - 2 + 3\n") | ||
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| /* | ||
| * Test that the input is parsed like ((a - b) + c). | ||
| * The parse tree should look like: | ||
| * | ||
| * plus | ||
| * / \ | ||
| * minus \ | ||
| * / \ \ | ||
| * 1 2 3 | ||
| */ | ||
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| val lexer = MiniCalcLexer(input) | ||
| val parser = MiniCalcParser(CommonTokenStream(lexer)) | ||
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| val plus = parser.expression() as MiniCalcParser.BinaryOperationContext | ||
| assertNotNull(plus.PLUS()) | ||
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| val minus = plus.left as MiniCalcParser.BinaryOperationContext | ||
| assertNotNull(minus.MINUS()) | ||
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| val one = minus.left as MiniCalcParser.IntLiteralContext | ||
| assertEquals(one.text, "1") | ||
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| val two = minus.right as MiniCalcParser.IntLiteralContext | ||
| assertEquals(two.text, "2") | ||
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| val three = plus.right as MiniCalcParser.IntLiteralContext | ||
| assertEquals(three.text, "3") | ||
| } |
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@yaccoff I've changed the grammar back to the way it was and also changed to test to show the even more fundamental error.
Here we see that, according to ANTLR, 1 - 2 + 3 is supposed to be parsed as (1 - 2) + 3.
But antlr-kotlin generates code that parses 1 - 2 + 3 as 1 - (2 + 3). It does not adhere to the ANTLR standard!
ANTLR's Parse Tree antlr-kotlin's Parse Tree
------------------- ---------------------------
plus minus
/ \ / \
minus \ / plus
/ \ \ / / \
1 2 3 1 2 3
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This bug basically makes antlr-kotlin unusable. Anyone can type 1 - 2 + 3 into a calculator (or Google) and get the answer: 2. But if I parse and evaluate that expression using antlr-kotlin, then I'll get -4!
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@yaccoff @ftomassetti I you can point me in the right direction of where the bug could be, I'd happily try to contribute a fix. |
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@ftomassetti I was able to apply the patch from @atsushieno and fix the failing unit test! Please take a look! |
tianyu
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@ftomassetti, will you take a look? |
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Included in #107 , so closing |
This PR contains a failing test showing that operator precedence is not respected.
No idea how to fix it, though :/Fixed!