lpeg.Cf

lpeg.Cf (patt, func)

If patt produces a list of captures C1 C2 ... Cn, this capture will produce the value func(...func(func(C1, C2), C3)..., Cn), that is, it will fold (or accumulate, or reduce) the captures from patt using function func.

This capture assumes that patt should produce at least one capture with at least one value (of any type), which becomes the initial value of an accumulator. (If you need a specific initial value, you may prefix a constant capture to patt.) For each subsequent capture LPeg calls func with this accumulator as the first argument and all values produced by the capture as extra arguments; the value returned by this call becomes the new value for the accumulator. The final value of the accumulator becomes the captured value.

As an example, the following pattern matches a list of numbers separated by commas and returns their addition:

-- matches a numeral and captures its value
number = lpeg.R"09"^1 / tonumber

-- matches a list of numbers, captures their values
list = number * ("," * number)^0

-- auxiliary function to add two numbers
function add (acc, newvalue) return acc + newvalue end

-- folds the list of numbers adding them
sum = lpeg.Cf(list, add)

-- example of use
print(sum:match("10,30,43")) --> 83