How to parse expression with an operator followed by two parameters

[DXie123]

I want to parse LaTex code like \frac{1}{2} (should be parsed to 1/2).

After read the tutorial on README, I found support for format like {parameter}operator{parameter}, but I didn't find a way to parse code like \frac{1}{2}, which is operator{parameter}{parameter}

I want to know if there is an appropriate way to handle this problem.

[renggli]

Please consider asking general questions like this on https://stackoverflow.com/questions/tagged/dart+petitparser

That said, the following code parses your example:

final arg = char('{') & digit() & char('}');
final frac = string('\\frac') & arg.star();

[DXie123]

Thanks for your answer

I do tried some similar ways to parse it:

final frac1 = string('\\frac{') & any().starLazy('}{') & char('}');  
final frac2 = string('\\frac{') & any().starGreedy('}{') & char('}');  

But none of them work in a more complex situation like \frac{\frac{1}{2}}{3}+\frac{1}{2}(should be (1/2)/3+1/2). Because there may have all kinds of code in parenthesis, I have to use any() in my project, but it always has some parenthesis mathcing problem.

[renggli]

To deal with nested grammars you need to recursively call yourself:

final frac = undefined();
final expr = frac | digit();
final arg = char('{') & expr & char('}');
frac.set(string('\\frac') & arg.star());

print(frac.parse('\\frac{\\frac{1}{2}}{3}')); 
// ==> Success[1:22]: [\frac, [[{, [\frac, [[{, 1, }], [{, 2, }]]], }], [{, 3, }]]]

This kind of recursive code is easier to write when using a GrammarDefinition.