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local re = require're'
local terror = {}
local function newError(l, msg)
table.insert(terror, { l = l, msg = msg } )
end
newError("errId", "Error: expecting an identifier")
newError("errComma", "Error: expecting ','")
local labelCode = {}
local labelMsg = {}
for k, v in ipairs(terror) do
labelCode[v.l] = k
labelMsg[v.l] = v.msg
end
re.setlabels(labelCode)
local p = re.compile([[
S <- Id List /{errId} ErrId /{errComma} ErrComma
List <- !. / Comma Id List
Id <- [a-z]+ / %{errId}
Comma <- ',' / %{errComma}
ErrId <- '' -> errId
ErrComma <- '' -> errComma
]], labelMsg)
print(p:match("a,b"))
print(p:match("a b"))
print(p:match(",b"))
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