local type = type local function mult(a, b) if a == 1 then return b end if b == 1 then return a end return {operator= '*', a, b} end local function infix_action(sym, a, b) if sym == '*' then return mult(a, b) else return {operator= sym, a, b} end end local function prefix_action(sym, a) return {operator= sym, a} end local function enum_action(id) return "%" .. id end local function func_eval_action(func_name, arg_expr) return {func = func_name, arg = arg_expr} end local function ident_action(id) return id end local function literal_action(name) return {literal= name} end -- return true iff expr is a variable (with enums or not). -- if it is a variable returns, in addition, the var_name and the enumeration flag local function is_variable(expr) if type(expr) == 'string' then local esc_name = string.match(expr, "^%%(.*)") return true, esc_name or expr, (esc_name ~= nil) else return false end end local function is_number(expr) return type(expr) == 'number' end return { infix = infix_action, ident = ident_action, literal = literal_action, prefix = prefix_action, enum = enum_action, func_eval = func_eval_action, number = function(x) return x end, exprlist = function(a, ls) if ls then ls[#ls+1] = a else ls = {a} end; return ls end, schema = function(x, y, conds, enums) return {x= x, y= y, conds= conds, enums= enums} end, is_variable = is_variable, is_number = is_number, }