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Where does nom's “$i” macro argument come from?



Unicorn Meta Zoo #1: Why another podcast?
Announcing the arrival of Valued Associate #679: Cesar Manara
Data science time! April 2019 and salary with experience
The Ask Question Wizard is Live!Casting pthread's start_routine argument with a macroOverloading Macro on Number of ArgumentsHow to implement a macro system into my LISPUnderstanding DEFER and OBSTRUCT macrosMacro call vs macro definition environment in JuliaStrange definitions of TRUE and FALSE macrosFixing “no rules expected the token” macro errorWhy does avr-gcc tell me about missing argument while expanding my [fancy] macro?How to use a type (ty) within a macro to construct a struct instance in Rust?PHP Internals: How does TSRMLS_FETCH Work?



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5















I'm trying to understand how Rust macro captures work and am looking at the nom parser library.



Location nom/src/bytes.rs declares macro tag! which captures with ($i:expr, $tag: expr).
However throughout the places where tag! is used it is used with only one argument, i.e. tag!("+").
Example: nom-lua52/op.rs. I've read tutorials about macros however this construct seems to be special.



It seems like the input $i is somehow implicit?










share|improve this question






























    5















    I'm trying to understand how Rust macro captures work and am looking at the nom parser library.



    Location nom/src/bytes.rs declares macro tag! which captures with ($i:expr, $tag: expr).
    However throughout the places where tag! is used it is used with only one argument, i.e. tag!("+").
    Example: nom-lua52/op.rs. I've read tutorials about macros however this construct seems to be special.



    It seems like the input $i is somehow implicit?










    share|improve this question


























      5












      5








      5








      I'm trying to understand how Rust macro captures work and am looking at the nom parser library.



      Location nom/src/bytes.rs declares macro tag! which captures with ($i:expr, $tag: expr).
      However throughout the places where tag! is used it is used with only one argument, i.e. tag!("+").
      Example: nom-lua52/op.rs. I've read tutorials about macros however this construct seems to be special.



      It seems like the input $i is somehow implicit?










      share|improve this question
















      I'm trying to understand how Rust macro captures work and am looking at the nom parser library.



      Location nom/src/bytes.rs declares macro tag! which captures with ($i:expr, $tag: expr).
      However throughout the places where tag! is used it is used with only one argument, i.e. tag!("+").
      Example: nom-lua52/op.rs. I've read tutorials about macros however this construct seems to be special.



      It seems like the input $i is somehow implicit?







      macros rust nom






      share|improve this question















      share|improve this question













      share|improve this question




      share|improve this question








      edited Mar 22 at 16:22









      loganfsmyth

      107k21229188




      107k21229188










      asked Jul 16 '18 at 18:08









      Konrad EiseleKonrad Eisele

      1,058816




      1,058816






















          1 Answer
          1






          active

          oldest

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          6














          The trick is that the tag!() macro call is inside the value! macro, which will match against tag! and pass it an additional parameter. This is described in the file implementing tag!.






          share|improve this answer


















          • 1





            Thanks, Now I see the trick: $submac!($i, $($args)*).

            – Konrad Eisele
            Jul 16 '18 at 18:28











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          1 Answer
          1






          active

          oldest

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          active

          oldest

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          active

          oldest

          votes









          6














          The trick is that the tag!() macro call is inside the value! macro, which will match against tag! and pass it an additional parameter. This is described in the file implementing tag!.






          share|improve this answer


















          • 1





            Thanks, Now I see the trick: $submac!($i, $($args)*).

            – Konrad Eisele
            Jul 16 '18 at 18:28















          6














          The trick is that the tag!() macro call is inside the value! macro, which will match against tag! and pass it an additional parameter. This is described in the file implementing tag!.






          share|improve this answer


















          • 1





            Thanks, Now I see the trick: $submac!($i, $($args)*).

            – Konrad Eisele
            Jul 16 '18 at 18:28













          6












          6








          6







          The trick is that the tag!() macro call is inside the value! macro, which will match against tag! and pass it an additional parameter. This is described in the file implementing tag!.






          share|improve this answer













          The trick is that the tag!() macro call is inside the value! macro, which will match against tag! and pass it an additional parameter. This is described in the file implementing tag!.







          share|improve this answer












          share|improve this answer



          share|improve this answer










          answered Jul 16 '18 at 18:24









          starbluestarblue

          45.7k1178138




          45.7k1178138







          • 1





            Thanks, Now I see the trick: $submac!($i, $($args)*).

            – Konrad Eisele
            Jul 16 '18 at 18:28












          • 1





            Thanks, Now I see the trick: $submac!($i, $($args)*).

            – Konrad Eisele
            Jul 16 '18 at 18:28







          1




          1





          Thanks, Now I see the trick: $submac!($i, $($args)*).

          – Konrad Eisele
          Jul 16 '18 at 18:28





          Thanks, Now I see the trick: $submac!($i, $($args)*).

          – Konrad Eisele
          Jul 16 '18 at 18:28



















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