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local lpeg = require"lpeglabel"
local R, S, P, V = lpeg.R, lpeg.S, lpeg.P, lpeg.V
local C, Cc, Ct, Cmt, Carg = lpeg.C, lpeg.Cc, lpeg.Ct, lpeg.Cmt, lpeg.Carg
local T, Lc, Rec = lpeg.T, lpeg.Lc, lpeg.Rec
local labels = {
{"NoExp", "no expression found"},
{"Extra", "extra characters found after the expression"},
{"ExpTerm", "expected a term after the operator"},
{"ExpExp", "expected an expression after the parenthesis"},
{"MisClose", "missing a closing ')' after the expression"},
}
local function labelindex(labname)
for i, elem in ipairs(labels) do
if elem[1] == labname then
return i
end
end
error("could not find label: " .. labname)
end
local function expect(patt, labname, recpatt)
local i = labelindex(labname)
local function recorderror(input, pos, errors)
table.insert(errors, {i, pos})
return true
end
if not recpatt then recpatt = P"" end
return Rec(patt, Cmt(Carg(1), recorderror) * recpatt)
end
local num = R("09")^1 / tonumber
local op = S("+-*/")
local function compute(tokens)
local result = tokens[1]
for i = 2, #tokens, 2 do
if tokens[i] == '+' then
result = result + tokens[i+1]
elseif tokens[i] == '-' then
result = result - tokens[i+1]
elseif tokens[i] == '*' then
result = result * tokens[i+1]
elseif tokens[i] == '/' then
result = result / tokens[i+1]
else
error('unknown operation: ' .. tokens[i])
end
end
return result
end
local g = P {
"Exp",
Exp = Ct(V"Term" * (C(op) * V"Operand")^0) / compute;
Operand = expect(V"Term", "ExpTerm", Cc(0));
Term = num + V"Group";
Group = "(" * V"InnerExp" * expect(")", "MisClose");
InnerExp = expect(V"Exp", "ExpExp", (P(1) - ")")^0 * Cc(0));
}
g = expect(g, "NoExp", P(1)^0) * expect(-P(1), "Extra")
local function eval(input)
local errors = {}
local result, label, suffix = g:match(input, 1, errors)
if #errors == 0 then
return result
else
local out = {}
for i, err in ipairs(errors) do
local pos = err[2]
local msg = labels[err[1]][2]
table.insert(out, "syntax error: " .. msg .. " (at index " .. pos .. ")")
end
return nil, table.concat(out, "\n")
end
end
print(eval "98-76*(54/32)")
--> 37.125
print(eval "(1+1-1*2/2")
--> syntax error: missing a closing ')' after the expression (at index 11)
print(eval "(1+)-1*(2/2)")
--> syntax error: expected a term after the operator (at index 4)
print(eval "(1+1)-1*(/2)")
--> syntax error: expected an expression after the parenthesis (at index 10)
print(eval "1+(1-(1*2))/2x")
--> syntax error: extra chracters found after the expression (at index 14)
print(eval "-1+(1-(1*2))/2")
--> syntax error: no expression found (at index 1)
print(eval "(1+1-1*(2/2+)-():")
--> syntax error: expected a term after the operator (at index 13)
--> syntax error: expected an expression after the parenthesis (at index 16)
--> syntax error: missing a closing ')' after the expression (at index 17)
--> syntax error: extra characters found after the expression (at index 17)
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