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local re = require 'relabel'
local errinfo = {
{"errUndef", "undefined"},
{"errId", "expecting an identifier"},
{"errComma", "expecting ','"},
}
local errmsgs = {}
local labels = {}
for i, err in ipairs(errinfo) do
errmsgs[i] = err[2]
labels[err[1]] = i
end
re.setlabels(labels)
local function calcline (s, i)
if i == 1 then return 1, 1 end
local rest, line = s:sub(1,i):gsub("[^\n]*\n", "")
local col = #rest
return 1 + line, col ~= 0 and col or 1
end
local g = re.compile[[
S <- Id List
List <- !. / (',' / %{errComma}) (Id / %{errId}) List
Id <- Sp [a-z]+
Comma <- Sp ','
Sp <- %s*
]]
function mymatch (g, s)
local r, e, sfail = g:match(s)
if not r then
local line, col = calcline(s, #s - #sfail)
local msg = "Error at line " .. line .. " (col " .. col .. "): "
return r, msg .. errmsgs[e] .. " before '" .. sfail .. "'"
end
return r
end
print(mymatch(g, "one,two"))
print(mymatch(g, "one two"))
print(mymatch(g, "one,\n two,\nthree,"))
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