Re: [Lpeg] Problem with Cf

[Pierre-Yves Gérardy <pygy79@...>]

On Sat, Apr 12, 2014 at 10:01 PM, Christophe Devalland
<christophe.devalland@gmail.com> wrote:
> Hello,
> function parenthese(expression)
>     return 'par{' .. expression .. '}'
> end
> [...]
>   -- the following line doesn't work as expected : 1    +    par{5}
>   -- Parentheses=Open*Cf(Exp,parenthese)*Close,

You're looking for the function capture, and Cf is the folding capture.

Replace `Cf(Exp,parenthese)` with `(Exp/parenthese)`, you'll get the
expected result.

`fold` is a higher level function also known as `reduce`.

for example, with `add` defined as `function(a, b) return a + b end`,
`fold(add, {1,2,3,4})` will return 10. Here's an implementation:

    function fold(func, array, first)
        local i0 = 1
        if first == nil then
            first, i0 = array[1], 2
        end
        local accumulator = first
        for i = i0, #array do
            accumulator = func(accumulator, array[i])
        end
        return accumulator
    end

The folding capture applies its second argument to the value of its
children captures in the same way.

On the other hand, the "function capture" applies the function once to
the values of all subcaptures.

—Pierre-Yves