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Questions tagged [tatsu]

Use the [tatsu] tag for all questions related to the TatSu or Grako parser generators.

TatSu (the successor to Grako) is a tool that takes grammars in a variation of EBNF as input, and outputs memoizing (Packrat) PEG parsers in Python.

TatSu can also compile a grammar stored in a string into a tatsu.grammars.Grammar object that can be used to parse any given input, much like the re module does with regular expressions.

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How do I handle negative numbers in a PEG grammar?

I'm trying to write a simple int expression parser using tatsu, a PEG-based Python parser generator. Here is my code: import tatsu grammar = r''' start = expression $ ; expression = add | sub | term ; add = expression '+' term ; sub…
itsadok
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How to generate standalone parser in Python?

I would like to generate a Python parser for a custom language. As I am new to parsing, my only requirement so far is that the generated module shall not depend on the generator. I learned Tatsu, as it can generate the parser as Python module. But…
Adam Trhon
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Error with tatsu : does not recognize the right grammar pattern

I am getting started with tatsu and I am trying to implement a grammar for the miniML language. Once my grammar successfully parsed, I tried to parse some little expressions to check that it was working ; however I discovered Tatsu was unable to…
Lara
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@name and @@keyword not working with rule annotations

I'm trying to use @@keyword and @name in my grammar but tatsu seems to ignore it if rules tagged @name are annotated. Am I missing something? To reproduce the behaviour, I provide the following example: This one works: import tatsu GRAMMAR =…
apio
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How to handle semantic failures in TatSu when parsing is correct?

I am trying to create a TatSu parser for a language containing C-like expressions. I have the following grammar rules for the expressions: identifier = /[a-zA-Z][A-Za-z0-9_]*/ ; expression = or_expr ; or_expr = …
Dominick Pastore
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Is it possible to continue parsing with other rules after an exception is raised in semantics?

Is it possible to fallback to other rules after an exception is raised in a semantic action? Like the following (contrived) scenario: var = /[a-zA-Z]+/; keyword = 'for' | 'in'; a = var:var | keyword:keyword; def a(ast): if (ast.var not in…
Sid Mani
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How to optimize this grammar rule?

I am implementing a grammar using the TatSu python library. My grammar is working OK but there is one rule that is eating quite a bit of time. On a block of around 3000 lines (part of a bigger grammar), if I take this full rule, it takes about 42s…
user4979733
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Tatsu: Rule Ordering

I am playing around with Tatsu to implement a parser for a language used in the semiconductor industry. This language requires that variables be defined before usage. So for example: SignalGroup { A: In; B: Out}; Pattern { V {A=1, B=1 } V…
user4979733
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Need help starting with Tatsu to parse grammar

I am getting a Tatsu error "tatsu.exceptions.FailedExpectingEndOfText: (1:1) Expecting end of text" running a test, using a grammar I supplied - it is not clear what the problem is. In essence, the statement calling the parser is: ast =…
Colin G
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How to match a pattern in Tatsu in a case insensitive manner

anybody knows how to recognize a pattern in Tatsu, in a case-insensitive way? The documentation says to: "Use (?i) in patterns that should ignore case." but I did not actually figure out how to use (?i) in my rule: graph = [ STRICT ] ( GRAPH…
Tommaso Mazza
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How to access TatSu parserinfo object

I've just started playing with TatSu and don't have much experience with it yet. I'm successfully parsing a small COBOL code snippet, but would like to access the details that are produced when parserinfo=True. Would anyone have some sample code I…
dreamer
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Generate random grammar expansions in TatSu (Python)

I'm writing an interpreter for a grammar parser generated with TatSu. I'm looking for a convenient way to generate use cases for my grammar, so I can write unit tests for my interpreter. Currently, I'm generating my test cases by hand. I wonder if…
apio
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Failure to match character that matches rule with PEG parser

I'm trying to parse Java-style floating point numbers (accepting underscores in the middle of digits) and have simplified the grammar presented in the Java spec: float_lit = [[DIGITS] '.'] DIGITS [FLOAT_EXP] [FLOAT_SUFFIX] ; DIGITS = /\d[\d_]*\d/ |…
Bruno Kim
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Tatsu no stopping at end of text

I trying to add some simple error handling to a DSL grammar in Tatsu. I wrote a simple grammar that parses input into either numbers or errors. @@grammar :: Nums start = wordlist $ ; wordlist = {word eol}+ ; eol = ':' ; word = | num:num …
tjgriffin
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Tatsu: How to validate/process arithmetic like expressions in semantic actions

I have a TatSu grammar where I am parsing arithmetic expressions like SignalGroup {ABUS='A3 + A2 + A1 + A0';}. Relevant grammar: #--------------------------------------------- SIGNAL GROUPS BLOCK…
user4979733
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