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local M = require 'macro'
local function eval (expr,was_expr)
expr = tostring(expr)
if was_expr then expr = "return "..expr end
local chunk = M.assert(loadstring(expr))
local ok, res = pcall(chunk)
if not ok then M.error("error evaluating "..res) end
return res
end
local function eval_line (get,was_expr)
local args = get:line()
return eval(args,was_expr)
end
local function grab (get)
local ilevel = 0
while true do
local t,v = get()
while t ~= '@' do t = get() end
t,v = get()
if v == 'if' then
ilevel = ilevel + 1
else -- 'end','elseif','else'
if ilevel > 0 and v == 'end' then
ilevel = ilevel - 1
elseif ilevel == 0 then return '@'..v end
end
end
end
M.define('@',function(get,put)
local t,v = get()
--~ print('got',t,v)
return put:iden(v..'_')
end)
local ifstack,push,pop = {},table.insert,table.remove
local function push_if (res)
--~ print 'push'
push(ifstack, not (res==false or res==nil))
end
local function pop_if ()
--~ print 'pop'
pop(ifstack)
end
M.define('if_',function(get)
local res = eval_line(get,true)
push_if(res)
if not res then
return grab(get)
end
end)
M.define('elseif_',function(get)
local res
if ifstack[#ifstack] then
res = false
else
res = eval_line(get,true)
pop_if()
push_if(res)
end
if not res then
return grab(get)
end
end)
M.define('else_',function(get)
if #ifstack == 0 then M.error("mismatched else") end
if ifstack[#ifstack] then
return grab(get)
end
end)
M.define('end_',function(get)
pop_if()
end)
M.define('let_',function(get)
eval_line(get)
end)
M.define('eval_(X)',function(X)
return tostring(eval(X,true))
end)
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