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 load, type, tonumber = load, type, tonumber
local concat = table.concat
local utfchar = utf.char
local find = string.find
local S, C, P, lpegmatch, lpegtsplitat = lpeg.S, lpeg.C, lpeg.P, lpeg.match, lpeg.tsplitat

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

local cmd          = tokens.commands

local scan_next    = token.scan_next or token.get_next
local scan_cmdchr  = token.scan_cmdchr_expanded

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 or token.get_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

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

implement { -- will be overloaded later
    name      = "writestatus",
    arguments = "2 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 = "2 strings",
    actions   = function(a,b)
        if a == b then
            ctx_firstoftwoarguments()
        else
            ctx_secondoftwoarguments()
        end
    end
}

implement {
    name      = "doifsame",
    arguments = "2 strings",
    actions   = function(a,b)
        if a == b then
            ctx_firstofoneargument()
        else
            ctx_gobbleoneargument()
        end
    end
}

implement {
    name      = "doifnotsame",
    arguments = "2 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.

do

    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 function expression()
        local w = 0
        local r = 1
        while true do
            local t = scan_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

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

end
