Where is the mistake in this parser? [closed]

I have begun on a PEG parser.

The goal is to build a grammar out of trees of combinators using sequence and either. I have some mistake in my sequence implementation, because I get false as the output from this instead of an empty stream.

-- <library>

-- Forward declare helper
local wrap

-- e: function | string
-- return: Parser (Stream -> Stream?)
function expect(e)
    local x = e
    if type(e) == "string" then
        x = function(n) return n == e end
    end
    return wrap(function(stream)
        if x( stream:first() ) then
            return stream:rest(), stream:first()
        else
            return false
        end
    end)
end

-- a, b: Parser
-- return: Parse (Stream -> Stream?)
function seq(a, b)
    return wrap(function(stream)
        local u = a(stream)
        if u then
            return b(stream)
        else
            return false
        end
    end)
end

-- wrappedCall(w, ...) is the same as w(...) for a value that has been
-- `wrap`pped
function wrappedCall(w, ...)
    return w["function"](...)
end

-- Allows + and * to be used as aliases for `either` and `sequence`.
-- function -> function+*
function wrap(f)
    local t = {["function"] = f}
    setmetatable(t, {

        __mul = seq,
        __call = wrappedCall})
    return t
end

-- Stream<element> -> element
function streamFirst(list)
    return list[1]
end

-- Stream -> Stream
function streamRest(list)
    local t = {unpack(list)}
    table.remove(t, 1)
    return Stream(t)
end

-- string -> Stream
function Stream(list)
    local s = {unpack(list)}
    s.first = streamFirst
    s.rest = streamRest
    return s
end

-- </library>

-- <client>

-- string -> boolean
function isLetter(s)
    return s:sub(1, 1):lower() ~= s:sub(1, 1):upper()
end

local name = expect(isLetter)
local open, close = expect("<"), expect(">")

local void = open * name * close 
local tokens = Stream {"<", "img", ">"}

print( void(tokens) )
-- I expect this to print `table: ABCDEF`, but I get `false`
-- </client>

Does anyone else have an idea of where I made a mistake? I regret not testing more incrementally...