if not modules then modules = { } end modules ['syst-lua'] = {
    version   = 1.001,
    comment   = "companion to syst-lua.mkiv",
    author    = "Hans Hagen, PRAGMA-ADE, Hasselt NL",
    copyright = "PRAGMA ADE / ConTeXt Development Team",
    license   = "see context related readme files"
}

local find = string.find
local S, C, P, lpegmatch, lpegtsplitat = lpeg.S, lpeg.C, lpeg.P, lpeg.match, lpeg.tsplitat

commands        = commands or { }
local commands  = commands
local context   = context
local implement = interfaces.implement

local ctx_protected_cs         = context.protected.cs -- more efficient
local ctx_firstoftwoarguments  = context.firstoftwoarguments
local ctx_secondoftwoarguments = context.secondoftwoarguments
local ctx_firstofoneargument   = context.firstofoneargument
local ctx_gobbleoneargument    = context.gobbleoneargument

local two_strings = interfaces.strings[2]

implement { -- will be overloaded later
    name      = "writestatus",
    arguments = two_strings,
    actions   = logs.status,
}

function commands.doifelse(b)
    if b then
        ctx_firstoftwoarguments()
    else
        ctx_secondoftwoarguments()
    end
end

function commands.doifelsesomething(b)
    if b and b ~= "" then
        ctx_firstoftwoarguments()
    else
        ctx_secondoftwoarguments()
    end
end

function commands.doif(b)
    if b then
        ctx_firstofoneargument()
    else
        ctx_gobbleoneargument()
    end
end

function commands.doifsomething(b)
    if b and b ~= "" then
        ctx_firstofoneargument()
    else
        ctx_gobbleoneargument()
    end
end

function commands.doifnot(b)
    if b then
        ctx_gobbleoneargument()
    else
        ctx_firstofoneargument()
    end
end

function commands.doifnotthing(b)
    if b and b ~= "" then
        ctx_gobbleoneargument()
    else
        ctx_firstofoneargument()
    end
end

commands.testcase = commands.doifelse -- obsolete

function commands.boolcase(b)
    context(b and 1 or 0)
end

function commands.doifelsespaces(str)
    if find(str,"^ +$") then
        ctx_firstoftwoarguments()
    else
        ctx_secondoftwoarguments()
    end
end

local pattern = lpeg.patterns.validdimen

function commands.doifelsedimenstring(str)
    if lpegmatch(pattern,str) then
        ctx_firstoftwoarguments()
    else
        ctx_secondoftwoarguments()
    end
end

local p_first = C((1-P(",")-P(-1))^0)

implement {
    name      = "firstinset",
    arguments = "string",
    actions   = function(str) context(lpegmatch(p_first,str or "")) end,
    public    = true,
}

implement {
    name      = "ntimes",
    arguments = { "string", "integer" },
    actions   = { string.rep, context }
}

implement {
    name      = "execute",
    arguments = "string",
    actions   = os.execute -- wrapped in sandbox
}

implement {
    name      = "doifelsesame",
    arguments = two_strings,
    actions   = function(a,b)
        if a == b then
            ctx_firstoftwoarguments()
        else
            ctx_secondoftwoarguments()
        end
    end
}

implement {
    name      = "doifsame",
    arguments = two_strings,
    actions   = function(a,b)
        if a == b then
            ctx_firstofoneargument()
        else
            ctx_gobbleoneargument()
        end
    end
}

implement {
    name      = "doifnotsame",
    arguments = two_strings,
    actions   = function(a,b)
        if a == b then
            ctx_gobbleoneargument()
        else
            ctx_firstofoneargument()
        end
    end
}

-- This is a bit of a joke as I never really needed floating point expressions (okay,
-- maybe only with scaling because there one can get numbers that are too large for
-- dimensions to deal with). Of course one can write a parser in \TEX\ speak but then
-- one also needs to implement a bunch of functions. It doesn't pay of so we just
-- stick to the next gimmick. It looks inefficient but performance is actually quite
-- efficient.

local concat = table.concat
local utfchar = utf.char
local load, type, tonumber = load, type, tonumber

local xmath    = xmath    or math
local xcomplex = xcomplex or { }

local cmd          = tokens.commands

local get_next     = token.get_next
local get_command  = token.get_command
local get_mode     = token.get_mode
local get_index    = token.get_index
local get_csname   = token.get_csname
local get_macro    = token.get_macro

local put_next     = token.put_next

local scan_token   = token.scan_token

local getdimen     = tex.getdimen
local getglue      = tex.getglue
local getcount     = tex.getcount
local gettoks      = tex.gettoks
local gettex       = tex.get

local context      = context
local dimenfactors = number.dimenfactors

local result = { "return " }
local word   = { }
local r      = 1
local w      = 0

local report = logs.reporter("system","expression")

local function unexpected(c)
    report("unexpected token %a",c)
end

local expression

if CONTEXTLMTXMODE == 0 then

    expression = function()
        local w = 0
        local r = 1
        while true do
            local t = get_next()
            local n = get_command(t)
            local c = cmd[n]
            -- todo, helper: returns number
            if c == "letter"  then
                w = w + 1 ; word[w] = utfchar(get_mode(t))
            else
                if w > 0 then
                    local s = concat(word,"",1,w)
                    local d = dimenfactors[s]
                    if d then
                        r = r + 1 ; result[r] = "*"
                        r = r + 1 ; result[r] = 1/d
                    else
                        if xmath[s] then
                            r = r + 1 ; result[r] = "xmath."
                        elseif xcomplex[s] then
                            r = r + 1 ; result[r] = "xcomplex."
                        end
                        r = r + 1 ; result[r] = s
                    end
                    w = 0
                end
                if     c == "other_char" then
                    r = r + 1 ; result[r] = utfchar(get_mode(t))
                elseif c == "spacer" then
                 -- r = r + 1 ; result[r] = " "
                elseif c == "relax" then
                    break
                elseif c == "assign_int" then
                    r = r + 1 ; result[r] = getcount(get_index(t))
                elseif c == "assign_dimen" then
                    r = r + 1 ; result[r] = getdimen(get_index(t))
                elseif c == "assign_glue" then
                    r = r + 1 ; result[r] = getglue(get_index(t))
                elseif c == "assign_toks" then
                    r = r + 1 ; result[r] = gettoks(get_index(t))
                elseif c == "char_given" or c == "math_given" or c == "xmath_given" then
                    r = r + 1 ; result[r] = get_mode(t)
                elseif c == "last_item" then
                    local n = get_csname(t)
                    if n then
                        local s = gettex(n)
                        if s then
                            r = r + 1 ; result[r] = s
                        else
                            unexpected(c)
                        end
                    else
                        unexpected(c)
                    end
                elseif c == "call" then
                    local n = get_csname(t)
                    if n then
                        local s = get_macro(n)
                        if s then
                            r = r + 1 ; result[r] = s
                        else
                            unexpected(c)
                        end
                    else
                        unexpected(c)
                    end
                elseif c == "the" or c == "convert" or c == "lua_expandable_call" then
                    put_next(t)
                    scan_token() -- expands
                else
                    unexpected(c)
                end
            end
        end
        local code = concat(result,"",1,r)
        local func = load(code)
        if type(func) == "function" then
            context(func())
        else
            report("invalid lua %a",code)
        end
    end

else

    local get_cmdchrcs             = tokens.get_cmdchrcs or token.get_cmdchrcs

    local letter_code              = cmd.letter
    local other_char_code          = cmd.other_char
    local spacer_code              = cmd.spacer
    local other_char_code          = cmd.other_char
    local relax_code               = cmd.relax
    local register_int_code        = cmd.register_int
    local internal_int_code        = cmd.internal_int
    local register_dimen_code      = cmd.register_dimen
    local internal_dimen_code      = cmd.internal_dimen
    local register_glue_code       = cmd.register_glue
    local internal_glue_code       = cmd.internal_glue
    local register_toks_code       = cmd.register_toks
    local internal_toks_code       = cmd.internal_toks
    local char_given_code          = cmd.char_given
    local math_given_code          = cmd.math_given
    local xmath_given_code         = cmd.xmath_given
    local some_item_code           = cmd.some_item
    local call_code                = cmd.call
    local the_code                 = cmd.the
    local convert_code             = cmd.convert
    local lua_expandable_call_code = cmd.lua_expandable_call

    local function unexpected(c)
        report("unexpected token %a",c)
    end

    expression = function()
        local w = 0
        local r = 1
        while true do
            local t = get_next()
            local n, i = get_cmdchrcs(t)
            if n == letter_code then
                w = w + 1 ; word[w] = utfchar(i)
            else
                if w > 0 then
                    -- we could use a metatable for all math, complex and factors
                    local s = concat(word,"",1,w)
                    local d = dimenfactors[s]
                    if d then
                        r = r + 1 ; result[r] = "*"
                        r = r + 1 ; result[r] = 1/d
                    else
                        if xmath[s] then
                            r = r + 1 ; result[r] = "xmath."
                        elseif xcomplex[s] then
                            r = r + 1 ; result[r] = "xcomplex."
                        end
                        r = r + 1 ; result[r] = s
                    end
                    w = 0
                end
                if     n == other_char_code then
                    r = r + 1 ; result[r] = utfchar(i)
                elseif n == spacer_code then
                -- r = r + 1 ; result[r] = " "
                elseif n == relax_code then
                    break
                elseif n == register_int_code or n == internal_int_code then
                    r = r + 1 ; result[r] = getcount(i)
                elseif n == register_dimen_code or n == internal_dimen_code then
                    r = r + 1 ; result[r] = getdimen(i)
                elseif n == register_glue_code or n == n == register_dimen_code_glue_code then
                    r = r + 1 ; result[r] = getglue(i)
                elseif n == register_toks_code or n == n == register_dimen_code_toks_code then
                    r = r + 1 ; result[r] = gettoks(i)
                elseif n == char_given_code or n == math_given_code or n == xmath_given_code then
                    r = r + 1 ; result[r] = i
                elseif n == some_item_code then
                    local n = get_csname(t)
                    if n then
                        local s = gettex(n)
                        if s then
                            r = r + 1 ; result[r] = s
                        else
                            unexpected(c)
                        end
                    else
                        unexpected(c)
                    end
                elseif n == call_code then
                    local n = get_csname(t)
                    if n then
                        local s = get_macro(n)
                        if s then
                            r = r + 1 ; result[r] = s
                        else
                            unexpected(c)
                        end
                    else
                        unexpected(c)
                    end
                elseif n == the_code or n == convert_code or n == lua_expandable_call_code then
                    put_next(t)
                    scan_token() -- expands
                else
                    unexpected(c)
                end
            end
        end
        local code = concat(result,"",1,r)
        local func = load(code)
        if type(func) == "function" then
            context(func())
        else
            report("invalid lua %a",code)
        end
    end

end

implement {
    public  = true,
    name    = "expression",
    actions = expression,
}