vimscript function for replacing pairs of parens

cycleParen.vim

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" Change matching pair of parens

nnoremap <leader>cp :call CycleParens()<CR>

function! CycleParens() abort
    let parens = ['[', '{', '(', ']', '}', ')']
    call CyclePairs(parens)
endfunction

function! CyclePairs(pairs) abort
    let cycleLen = len(a:pairs)
    let halfCycle = cycleLen / 2
    let currentChar = strcharpart(getline('.')[col('.') - 1:], 0, 1)
    let charIndex = index(a:pairs, currentChar)
    if charIndex == -1 | return | endif
    if charIndex + 1 == cycleLen || charIndex + 1 == halfCycle
        let nextChar = charIndex + 1 - halfCycle
    else
        let nextChar = charIndex + 1
    endif
    execute 'normal! %r' . a:pairs[(nextChar + halfCycle) % cycleLen] .
                \ '``r' . a:pairs[nextChar]
endfunction