make a json object and write it to a file

expand-write.kak

# try for example:
# :expand-write state.json '{"selections":%val{selections},"filetype":%opt{filetype},"yank":%reg{"}}'

def expand -params 1 %{
    eval -no-hooks -draft %{
        try %{
            edit -scratch *expand*
        }
    }
    eval -save-regs s %{
        eval -no-hooks -buffer *expand* %{
            reg '"' "%arg{1}"
            exec -no-hooks '%R'
            make-search-and-replace-script
        }
        eval -no-hooks "%reg{s}"
    }
}

def expand-write -params 2 %{
    expand %arg{2}
    eval -no-hooks -buffer *expand* %{
        write %arg{1}
        delete-buffer!
    }
}

def make-search-and-replace-script %{
    reg s ''
    exec -no-hooks '%s%\w*?\{.*?\}<ret>'
    eval -no-hooks -itersel %{
        reg s "replace-eval '%val{selection}' %val{selection};%reg{s}"
    }
}

def replace-eval -params 2 %{
    eval -no-hooks -save-regs qv %{
        set-register q "%arg{1}"
        set-register v "%arg{2}"
        eval -no-hooks -buffer *expand* %{
            exec -no-hooks -save-regs '' '%s\Q<c-r>q<ret>"v<a-R>Zi"<esc>'
            try %{ exec -no-hooks 'zs["\\]<ret>i\<esc>' }
            try %{ exec -no-hooks 'zs\n<ret>c\n<esc>' }
            try %{ exec -no-hooks 'zs\t<ret>c\t<esc>' }
            exec -no-hooks 'za"<esc>'
        }
    }
}