Lua程序设计第4版第18章练习答案

--18.1 18.2

function fromto(n,m)
    local k = 0
    return function()
        k = k+m
        return n[k]
    end
end
local n = {1,2,3}
local m = 2
for i in fromto(n,m) do
    if i ==nil then
        break
    end
    print(i)
end

--18.3

function allWords(fname)
    io.input(fname)
    local d = {}
    local r = {}
    local pos = 1
    local rpos = 0
    local line = io.read()
    while line do
        local word,p = string.match(line,"(%w+)()",pos)
        if word then
            d[word] = d[word]==nil and 1 or d[word]+1
            pos = p
        else
            line = io.read()
            pos = 1
        end
    end
    local cnt = 1
    for k,v in pairs(d) do
        if v==1 then
            r[cnt] = k
            cnt = cnt+1
        end
    end
    return function()
        rpos = rpos+1
        return r[rpos]
    end
end
for word in allWords("data.lua") do
    print(word)
end