Actions

Actions are a means to attach arbitrary pieces of code to patterns. Actions are executed upon successful execution of the attached pattern

The Basics

Actions are functors that may take an argument and may return a value. They can be attached to parsers using the indexing operator: [].

Example:

auto action = [](){std::cout << "pattern has matched!" << std::endl;};
auto pattern = *char_()[action];

Taking parameters

If the functor takes a parameter, it will behave as the destination of the attached parser.¹

Example:

auto action = [](char c){std::cout << "found a letter: " << c << std::endl;};
auto pattern = *char_()[action];

Returning a value

If the functor returns a value, that value will be assigned to whatever destination is provided to the action.

Example:

auto action = [](unsigned char c){return std::toupper(c);};
auto pattern = *char_()[action];

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1. In order to do that, Abulafia needs to create a temporary instance of the parameter for the parser to decode into. This means that the type of the parameter has to be default-constructible. ↩