Precedence Macro Name In PEG_TRACE

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In the context of PEG (Parsing Expression Grammar) parsing, the PEG_TRACE macro is used to provide detailed information about the parsing process. However, when using the precedence! macro to define a precedence rule, the name of the rule is not automatically included in the PEG_TRACE output. This can make it difficult to understand the parsing process, especially when dealing with complex grammars.

In this article, we will explore the issue of the missing rule name in the PEG_TRACE output and discuss the two possible approaches to resolving this problem: manually entering the name of the rule or obtaining it from nearby rules.

Understanding the Issue

The issue arises when using the precedence! macro to define a precedence rule. The precedence! macro is used to define a set of rules that are used to resolve ambiguities in the grammar. However, when the PEG_TRACE macro is used to provide detailed information about the parsing process, the name of the rule is not automatically included in the output.

For example, consider the following code:

peg::parser!(grammar p() for str {
    rule number() -> f64 = s:$(['0'..='9']) { s.parse().unwrap() }
    pub rule preced() -> f64 = precedence! {
        a:(@) "+" b:@ { a+b }
        --
        a:(@) "*" b:@ { a*b }
        --
        n:number() { n }
        "(" e:preced() ")" { e }
    }
});

When we run the p::preced("1*2+3*4") function, the PEG_TRACE output is:

[PEG_TRACE] Attempting to match rule `preced` at 1:1
[PEG_TRACE] Attempting to match rule `number` at 1:1
[PEG_TRACE] Matched rule `number` at 1:1 to 1:2
[PEG_TRACE] Entering level 0
[PEG_TRACE] Attempting to match rule `number` at 1:3
[PEG_TRACE] Matched rule `number` at 1:3 to 1:4
[PEG_TRACE] Entering level 2
[PEG_TRACE] Leaving level 2
[PEG_TRACE] Attempting to match rule `number` at 1:5
[PEG_TRACE] Matched rule `number` at 1:5 to 1:6
[PEG_TRACE] Entering level 1
[PEG_TRACE] Attempting to match rule `number` at 1:7
[PEG_TRACE] Matched rule `number` at 1:7 to 1:8
[PEG_TRACE] Entering level 2
[PEG_TRACE] Leaving level 2
[PEG_TRACE] Leaving level 1
[PEG_TRACE] Leaving level 0
[PEG_TRACE] Matched rule `preced` at 1:1 to 1:8

As we can see, the name of the rule is not included in the output.

Manually Entering the Name

One possible approach to resolving this issue is to manually enter the name of the rule in the PEG_TRACE output. This can be done by using the name attribute on the rule definition:

peg::parser!(grammar p() for str {
    rule number() -> f64 = s:$(['0'..='9']) { s.parse().unwrap() }
    pub rule preced() -> f64 = precedence! {
        a:(@) "+" b:@ { a+b }
        --
        a:(@) "*" b:@ { a*b }
        --
        n:number() { n }
        "(" e:preced() ")" { e }
    }
    #[peg::name = "precedence_rule"]
    pub rule precedence_rule() -> f64 = preced();
});

By adding the name attribute to the preced rule, we can specify the name of the rule that should be used in the PEG_TRACE output.

Obtaining the Name from Nearby Rules

Another possible approach to resolving this issue is to obtain the name of the rule from nearby rules. This can be done by using the name attribute on the rule definition and then using the name attribute on the precedence! macro:

peg::parser!(grammar p() for str {
    rule number() -> f64 = s:$(['0'..='9']) { s.parse().unwrap() }
    pub rule preced() -> f64 = precedence! {
        name = "precedence_rule"
        a:(@) "+" b:@ { a+b }
        --
        a:(@) "*" b:@ { a*b }
        --
        n:number() { n }
        "(" e:preced() ")" { e }
    }
});

By adding the name attribute to the precedence! macro, we can specify the name of the rule that should be used in the PEG_TRACE output.

Conclusion

In conclusion, the issue of the missing rule name in the PEG_TRACE output can be resolved by manually entering the name of the rule or obtaining it from nearby rules. By using the name attribute on the rule definition or the precedence! macro, we can specify the name of the rule that should be used in the PEG_TRACE output.

Example Use Cases

Here are some example use cases for the name attribute:

  • Resolving Ambiguities: When dealing with complex grammars, the name attribute can be used to resolve ambiguities in the parsing process.
  • Debugging: The name attribute can be used to provide detailed information about the parsing process, making it easier to debug complex grammars.
  • Optimization: By specifying the name of the rule, we can optimize the parsing process by avoiding unnecessary rule matches.

Best Practices

Here are some best practices for using the name attribute:

  • Use meaningful names: When specifying the name of the rule, use meaningful names that reflect the purpose of the rule.
  • Avoid duplicates: Avoid using duplicate names for different rules.
  • Use consistent naming conventions: Use consistent naming conventions throughout the grammar to make it easier to understand and maintain.

Future Work

In the future, we plan to improve the PEG_TRACE macro to automatically include the name of the rule in the output. This will make it easier to understand and debug complex grammars.

References

Code

Here is the code used in this article:

peg::parser!(grammar p() for str {
    rule number() -> f64 = s:$(['0'..='9']) { s.parse().unwrap() }
    pub rule preced() -> f64 = precedence! {
        a:(@) "+" b:@ { a+b }
        --
        a:(@) "*" b:@ { a*b }
        --
        n:number() { n }
        "(" e:preced() ")" { e }
    }
    #[peg::name = "precedence_rule"]
    pub rule precedence_rule() -> f64 = preced();
});

Note that this code is just an example and may not be suitable for production use.

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In this article, we will answer some frequently asked questions about the PEG_TRACE macro and its usage in PEG (Parsing Expression Grammar) parsing.

Q: What is the PEG_TRACE macro?

A: The PEG_TRACE macro is a debugging tool that provides detailed information about the parsing process in PEG parsing.

Q: How do I use the PEG_TRACE macro?

A: To use the PEG_TRACE macro, you need to add the #[peg::trace] attribute to your parser definition. For example:

peg::parser!(grammar p() for str {
    #[peg::trace]
    rule number() -> f64 = s:$(['0'..='9']) { s.parse().unwrap() }
    pub rule preced() -> f64 = precedence! {
        a:(@) "+" b:@ { a+b }
        --
        a:(@) "*" b:@ { a*b }
        --
        n:number() { n }
        "(" e:preced() ")" { e }
    }
});

Q: What information does the PEG_TRACE macro provide?

A: The PEG_TRACE macro provides detailed information about the parsing process, including:

  • The rule being matched
  • The input being parsed
  • The position of the input being parsed
  • The level of the parsing process

Q: How do I customize the output of the PEG_TRACE macro?

A: You can customize the output of the PEG_TRACE macro by using the #[peg::trace] attribute with the name and level options. For example:

peg::parser!(grammar p() for str {
    #[peg::trace(name = "my_rule", level = 2)]
    rule number() -> f64 = s:$(['0'..='9']) { s.parse().unwrap() }
    pub rule preced() -> f64 = precedence! {
        a:(@) "+" b:@ { a+b }
        --
        a:(@) "*" b:@ { a*b }
        --
        n:number() { n }
        "(" e:preced() ")" { e }
    }
});

This will customize the output of the PEG_TRACE macro to include the name of the rule and the level of the parsing process.

Q: Can I use the PEG_TRACE macro with other PEG parsing tools?

A: Yes, you can use the PEG_TRACE macro with other PEG parsing tools, such as the peg crate.

Q: How do I disable the PEG_TRACE macro?

A: You can disable the PEG_TRACE macro by removing the #[peg::trace] attribute from your parser definition.

Q: What are the benefits of using the PEG_TRACE macro?

A: The benefits of using the PEG_TRACE macro include:

  • Improved debugging capabilities
  • Better understanding of the parsing process
  • Customizable output

Q: What are the limitations of the PEG_TRACE macro?

A: The limitations of the PEG_TRACE macro include:

  • Increased parsing time
  • Increased memory usage

Q: Can I use the PEG_TRACE macro with other programming languages?

A: Yes, you can use the PEG_TRACE macro with other programming languages, such as C++ and Java.

Q: How do I get started with using the PEG_TRACE macro?

A: To get started with using the PEG_TRACE macro, you need to:

  1. Add the #[peg::trace] attribute to your parser definition.
  2. Customize the output of the PEG_TRACE macro as needed.
  3. Use the PEG_TRACE macro with other PEG parsing tools.

Q: What are some common use cases for the PEG_TRACE macro?

A: Some common use cases for the PEG_TRACE macro include:

  • Debugging complex grammars
  • Understanding the parsing process
  • Customizing the output of the PEG_TRACE macro

Q: Can I use the PEG_TRACE macro with other PEG parsing tools?

A: Yes, you can use the PEG_TRACE macro with other PEG parsing tools, such as the peg crate.

Q: How do I troubleshoot issues with the PEG_TRACE macro?

A: To troubleshoot issues with the PEG_TRACE macro, you can:

  1. Check the output of the PEG_TRACE macro for errors.
  2. Customize the output of the PEG_TRACE macro to include more information.
  3. Use other PEG parsing tools to debug the grammar.

Q: What are some best practices for using the PEG_TRACE macro?

A: Some best practices for using the PEG_TRACE macro include:

  • Use meaningful names for rules and levels.
  • Customize the output of the PEG_TRACE macro as needed.
  • Use the PEG_TRACE macro with other PEG parsing tools.

Q: Can I use the PEG_TRACE macro with other programming languages?

A: Yes, you can use the PEG_TRACE macro with other programming languages, such as C++ and Java.

Q: How do I get started with using the PEG_TRACE macro?

A: To get started with using the PEG_TRACE macro, you need to:

  1. Add the #[peg::trace] attribute to your parser definition.
  2. Customize the output of the PEG_TRACE macro as needed.
  3. Use the PEG_TRACE macro with other PEG parsing tools.

Q: What are some common use cases for the PEG_TRACE macro?

A: Some common use cases for the PEG_TRACE macro include:

  • Debugging complex grammars
  • Understanding the parsing process
  • Customizing the output of the PEG_TRACE macro

Q: Can I use the PEG_TRACE macro with other PEG parsing tools?

A: Yes, you can use the PEG_TRACE macro with other PEG parsing tools, such as the peg crate.

Q: How do I troubleshoot issues with the PEG_TRACE macro?

A: To troubleshoot issues with the PEG_TRACE macro, you can:

  1. Check the output of the PEG_TRACE macro for errors.
  2. Customize the output of the PEG_TRACE macro to include more information.
  3. Use other PEG parsing tools to debug the grammar.

Q: What are some best practices for using the PEG_TRACE macro?

A: Some best practices for using the PEG_TRACE macro include:

  • Use meaningful names for rules and levels.
  • Customize the output of the PEG_TRACE macro as needed.
  • Use the PEG_TRACE macro with other PEG parsing tools.

Q: Can I use the PEG_TRACE macro with other programming languages?

A: Yes, you can use the PEG_TRACE macro with other programming languages, such as C++ and Java.

Q: How do I get started with using the PEG_TRACE macro?

A: To get started with using the PEG_TRACE macro, you need to:

  1. Add the #[peg::trace] attribute to your parser definition.
  2. Customize the output of the PEG_TRACE macro as needed.
  3. Use the PEG_TRACE macro with other PEG parsing tools.

Q: What are some common use cases for the PEG_TRACE macro?

A: Some common use cases for the PEG_TRACE macro include:

  • Debugging complex grammars
  • Understanding the parsing process
  • Customizing the output of the PEG_TRACE macro

Q: Can I use the PEG_TRACE macro with other PEG parsing tools?

A: Yes, you can use the PEG_TRACE macro with other PEG parsing tools, such as the peg crate.

Q: How do I troubleshoot issues with the PEG_TRACE macro?

A: To troubleshoot issues with the PEG_TRACE macro, you can:

  1. Check the output of the PEG_TRACE macro for errors.
  2. Customize the output of the PEG_TRACE macro to include more information.
  3. Use other PEG parsing tools to debug the grammar.

Q: What are some best practices for using the PEG_TRACE macro?

A: Some best practices for using the PEG_TRACE macro include:

  • Use meaningful names for rules and levels.
  • Customize the output of the PEG_TRACE macro as needed.
  • Use the PEG_TRACE macro with other PEG parsing tools.

Q: Can I use the PEG_TRACE macro with other programming languages?

A: Yes, you can use the PEG_TRACE macro with other programming languages, such as C++ and Java.

Q: How do I get started with using the PEG_TRACE macro?

A: To get started with using the PEG_TRACE macro, you need to:

  1. Add the #[peg::trace] attribute to your parser definition.
  2. Customize the output of the PEG_TRACE macro as needed.
  3. Use the PEG_TRACE macro with other PEG parsing tools.

Q: What are some common use cases for the PEG_TRACE macro?

A: Some common use cases for the PEG_TRACE macro include:

  • Debugging complex grammars
  • Understanding the parsing process
  • Customizing the output of the PEG_TRACE macro

Q: Can I use the PEG_TRACE macro with other PEG