mirror of
https://github.com/falcosecurity/falco.git
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355 lines
9.0 KiB
Lua
355 lines
9.0 KiB
Lua
--[[
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Sysdig grammar and parser.
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Much of the scaffolding and helpers was deriverd Andre Murbach Maidl's Lua parser (https://github.com/andremm/lua-parser).
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Parses regular filters following the existing sysdig filter syntax (*), as well as "macro" definitions. Macro definitions are written like:
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inbound: (syscall.type=listen and evt.dir='>') or (syscall.type=accept and evt.dir='<')
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(*) There currently one known difference with the syntax implemented in libsinsp:
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- In libsinsp, field names cannot start with 'a', 'o', or 'n'. With this parser they can
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--]]
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local parser = {}
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local lpeg = require "lpeg"
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lpeg.locale(lpeg)
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local P, S, V = lpeg.P, lpeg.S, lpeg.V
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local C, Carg, Cb, Cc = lpeg.C, lpeg.Carg, lpeg.Cb, lpeg.Cc
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local Cf, Cg, Cmt, Cp, Ct = lpeg.Cf, lpeg.Cg, lpeg.Cmt, lpeg.Cp, lpeg.Ct
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local alpha, digit, alnum = lpeg.alpha, lpeg.digit, lpeg.alnum
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local xdigit = lpeg.xdigit
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local space = lpeg.space
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-- error message auxiliary functions
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-- creates an error message for the input string
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local function syntaxerror (errorinfo, pos, msg)
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local error_msg = "%s: syntax error, %s"
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return string.format(error_msg, pos, msg)
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end
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-- gets the farthest failure position
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local function getffp (s, i, t)
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return t.ffp or i, t
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end
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-- gets the table that contains the error information
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local function geterrorinfo ()
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return Cmt(Carg(1), getffp) * (C(V"OneWord") + Cc("EOF")) /
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function (t, u)
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t.unexpected = u
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return t
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end
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end
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-- creates an errror message using the farthest failure position
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local function errormsg ()
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return geterrorinfo() /
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function (t)
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local p = t.ffp or 1
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local msg = "unexpected '%s', expecting %s"
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msg = string.format(msg, t.unexpected, t.expected)
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return nil, syntaxerror(t, p, msg)
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end
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end
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-- reports a syntactic error
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local function report_error ()
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return errormsg()
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end
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--- sets the farthest failure position and the expected tokens
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local function setffp (s, i, t, n)
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if not t.ffp or i > t.ffp then
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t.ffp = i
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t.list = {} ; t.list[n] = n
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t.expected = "'" .. n .. "'"
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elseif i == t.ffp then
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if not t.list[n] then
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t.list[n] = n
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t.expected = "'" .. n .. "', " .. t.expected
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end
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end
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return false
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end
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local function updateffp (name)
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return Cmt(Carg(1) * Cc(name), setffp)
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end
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-- regular combinators and auxiliary functions
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local function token (pat, name)
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return pat * V"Skip" + updateffp(name) * P(false)
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end
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local function symb (str)
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return token (P(str), str)
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end
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local function kw (str)
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return token (P(str) * -V"idRest", str)
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end
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local function list (pat, sep)
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return Ct(pat^0 * (sep * pat^0)^0) / function(elements) return {type = "List", elements=elements} end
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end
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local function terminal (tag)
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return token(V(tag), tag) / function (tok) return { type = tag, value = tok} end
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end
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local function unaryboolop (op, e)
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return { type = "UnaryBoolOp", operator = op, argument = e }
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end
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local function unaryrelop (e, op)
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return { type = "UnaryRelOp", operator = op, argument = e }
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end
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local function binaryop (e1, op, e2)
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if not op then
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return e1
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else
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return { type = "BinaryBoolOp", operator = op, left = e1, right = e2 }
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end
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end
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local function bool (pat, sep)
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return Cf(pat * Cg(sep * pat)^0, binaryop)
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end
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local function rel (left, sep, right)
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return left * sep * right / function(e1, op, e2) return { type = "BinaryRelOp", operator = op, left = e1, right = e2 } end
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end
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local function fix_str (str)
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str = string.gsub(str, "\\a", "\a")
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str = string.gsub(str, "\\b", "\b")
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str = string.gsub(str, "\\f", "\f")
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str = string.gsub(str, "\\n", "\n")
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str = string.gsub(str, "\\r", "\r")
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str = string.gsub(str, "\\t", "\t")
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str = string.gsub(str, "\\v", "\v")
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str = string.gsub(str, "\\\n", "\n")
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str = string.gsub(str, "\\\r", "\n")
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str = string.gsub(str, "\\'", "'")
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str = string.gsub(str, '\\"', '"')
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str = string.gsub(str, '\\\\', '\\')
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return str
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end
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-- grammar
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local function filter(e)
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return {type = "Filter", value=e}
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end
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local function macro (name, filter)
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return {type = "MacroDef", name = name, value = filter}
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end
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local G = {
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V"Start", -- Entry rule
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Start = (V"MacroDef" / macro + V"Filter" / filter) * -1 + report_error();
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-- Grammar
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Filter = V"OrExpression";
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OrExpression =
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bool(V"AndExpression", V"OrOp");
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AndExpression =
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bool(V"NotExpression", V"AndOp");
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NotExpression =
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V"UnaryBoolOp" * V"NotExpression" / unaryboolop +
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V"ExistsExpression";
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ExistsExpression =
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terminal "FieldName" * V"ExistsOp" / unaryrelop +
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V"MacroExpression";
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MacroExpression =
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terminal "Macro" +
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V"RelationalExpression";
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RelationalExpression =
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rel(terminal "FieldName", V"RelOp", V"Value") +
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rel(terminal "FieldName", V"InOp", V"InList") +
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V"PrimaryExp";
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PrimaryExp = symb("(") * V"Filter" * symb(")");
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MacroDef = (C(V"Macro") * V"Skip" * V"Colon" * (V"Filter"));
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-- Terminals
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Value = terminal "Number" + terminal "String" + terminal "BareString";
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InList = symb("(") * list(V"Value", symb(",")) * symb(")");
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-- Lexemes
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Space = space^1;
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Skip = (V"Space")^0;
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idStart = alpha + P("_");
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idRest = alnum + P("_");
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Identifier = V"idStart" * V"idRest"^0;
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Macro = V"idStart" * V"idRest"^0 * -P".";
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FieldName = V"Identifier" * (P"." + V"Identifier")^1;
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Name = C(V"Identifier") * -V"idRest";
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Hex = (P("0x") + P("0X")) * xdigit^1;
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Expo = S("eE") * S("+-")^-1 * digit^1;
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Float = (((digit^1 * P(".") * digit^0) +
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(P(".") * digit^1)) * V"Expo"^-1) +
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(digit^1 * V"Expo");
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Int = digit^1;
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Number = C(V"Hex" + V"Float" + V"Int") /
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function (n) return tonumber(n) end;
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String = (P'"' * C(((P'\\' * P(1)) + (P(1) - P'"'))^0) * P'"' + P"'" * C(((P"\\" * P(1)) + (P(1) - P"'"))^0) * P"'") / function (s) return fix_str(s) end;
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BareString = C(((P(1) - S' (),'))^1);
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OrOp = kw("or") / "or";
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AndOp = kw("and") / "and";
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Colon = kw(":");
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RelOp = symb("=") / "eq" +
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symb("==") / "eq" +
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symb("!=") / "ne" +
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symb("<=") / "le" +
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symb(">=") / "ge" +
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symb("<") / "lt" +
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symb(">") / "gt" +
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symb("contains") / "contains" +
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symb("icontains") / "icontains";
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InOp = kw("in") / "in";
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UnaryBoolOp = kw("not") / "not";
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ExistsOp = kw("exists") / "exists";
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-- for error reporting
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OneWord = V"Name" + V"Number" + V"String" + P(1);
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}
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function map(f, arr)
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local res = {}
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for i,v in ipairs(arr) do
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res[i] = f(v)
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end
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return res
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end
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function foldr(f, acc, arr)
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for i,v in pairs(arr) do
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acc = f(acc, v)
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end
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return acc
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end
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--[[
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Traverses the AST and replaces `in` relational expressions with a sequence of ORs.
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For example, `a.b in [1, 2]` is expanded to `a.b = 1 or a.b = 2` (in ASTs)
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--]]
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function expand_in(node)
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local t = node.type
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if t == "Filter" then
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expand_in(node.value)
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elseif t == "UnaryBoolOp" then
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expand_in(node.argument)
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elseif t == "BinaryBoolOp" then
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expand_in(node.left)
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expand_in(node.right)
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elseif t == "BinaryRelOp" and node.operator == "in" then
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if (table.maxn(node.right.elements) == 0) then
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error ("In list with zero elements")
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end
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local mapper = function(element)
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return {
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type = "BinaryRelOp",
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operator = "eq",
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left = node.left,
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right = element
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}
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end
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local equalities = map(mapper, node.right.elements)
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local lasteq = equalities[table.maxn(equalities)]
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equalities[table.maxn(equalities)] = nil
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local folder = function(left, right)
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return {
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type = "BinaryBoolOp",
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operator = "or",
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left = left,
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right = right
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}
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end
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lasteq = foldr(folder, lasteq, equalities)
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node.type=lasteq.type
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node.operator=lasteq.operator
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node.left=lasteq.left
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node.right=lasteq.right
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end
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end
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function print_ast(node, level)
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local t = node.type
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local prefix = string.rep(" ", level*2)
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level = level + 1
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if t == "Filter" then
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print_ast(node.value, level)
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elseif t == "BinaryBoolOp" or t == "BinaryRelOp" then
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print(prefix..node.operator)
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print_ast(node.left, level)
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print_ast(node.right, level)
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elseif t == "UnaryRelOp" or t == "UnaryBoolOp" then
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print (prefix..node.operator)
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print_ast(node.argument, level)
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elseif t == "List" then
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print(prefix.. "List: ")
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for i, v in ipairs(node.elements) do
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print_ast(v, level)
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end
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elseif t == "FieldName" or t == "Number" or t == "String" or t == "BareString" or t == "Macro" then
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print (prefix..t.." "..node.value)
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elseif t == "MacroDef" then
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-- don't print for now
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else
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error ("Unexpected type: "..t)
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end
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end
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function parser.parse (subject)
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local errorinfo = { subject = subject }
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lpeg.setmaxstack(1000)
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local ast, error_msg = lpeg.match(G, subject, nil, errorinfo)
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if (error_msg) then
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return ast, error_msg
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end
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expand_in(ast)
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return ast, error_msg
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end
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return parser
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