lua metatable __lt __le __eq forced boolean conversion of return value
- by chris g.
Overloading __eq, __lt, and __le in a metatable always converts the returning value to a boolean.
Is there a way to access the actual return value?
This would be used in the following little lua script to create an expression tree for an argument
usage:
print(_.a + _.b - _.c * _.d + _.a)
-> prints "(((a+b)-(c*d))+a)" which is perfectly what I would like to have
but it doesn't work for print(_.a == _.b) since the return value gets converted to a boolean
ps: print should be replaced later with a function processing the expression tree
-- snip from lua script --
function binop(op1,op2, event)
if op1[event] then return op1[event](op1, op2) end
if op2[event] then return op2[event](op1, op2) end
return nil
end
function eq(op1, op2)return binop(op1,op2, "eq") end
...
function div(op1, op2)return binop(op1,op2, "div") end
function exprObj(tostr)
expr = { eq = binExpr("=="), lt = binExpr("<"), le = binExpr("<="), add = binExpr("+"), sub=binExpr("-"), mul = binExpr("*"), div= binExpr("/") }
setmetatable(expr, { __eq = eq, __lt = lt, __le = le, __add = add, __sub = sub, __mul = mul, __div = div, __tostring = tostr })
return expr
end
function binExpr(exprType)
function binExprBind(lhs, rhs)
return exprObj(function(op) return "(" .. tostring(lhs) .. exprType .. tostring(rhs) .. ")" end)
end
return binExprBind
end
function varExpr(obj, name)
return exprObj(function() return name end)
end
_ = {}
setmetatable(_, { __index = varExpr })
-- snap --
Modifing the lua vm IS an option, however it would be nice if I could use an official release
