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local m = require"lpeglabel"
local re = require"relabel"
local num = m.R("09")^1 / tonumber
local op = m.S("+-")
local labels = {}
local function newError(lab, msg, psync, pcap)
psync = psync or m.P(-1)
pcap = pcap or m.P""
labels[lab] = { msg = msg, psync = psync, pcap = pcap }
end
newError("ExpTermFirst", "expected an expression", op + ")", m.Cc(1000))
newError("ExpTermOp", "expected a term after the operator", op + ")", m.Cc(1000))
newError("MisClose", "missing a closing ')' after the expression", m.P")")
newError("Extra", "extra characters found after the expression")
local errors, subject
local function expect(patt, lab)
return patt + m.T(lab)
end
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]
else
error('unknown operation: ' .. tokens[i])
end
end
return result
end
function recorderror(pos, lab)
local line, col = re.calcline(subject, pos)
table.insert(errors, { line = line, col = col, msg = labels[lab].msg })
end
function record (labname)
return (m.Cp() * m.Cc(labname)) / recorderror
end
function sync (p)
return (-p * m.P(1))^0
end
function defaultValue (p)
return p or m.Cc(1000)
end
local g = {
"Exp",
Exp = m.Ct(m.V"OperandFirst" * (m.C(op) * m.V"Operand")^0) / compute,
OperandFirst = expect(m.V"Term", "ExpTermFirst"),
Operand = expect(m.V"Term", "ExpTermOp"),
Term = num + m.V"Group",
Group = "(" * m.V"Exp" * expect(")", "MisClose"),
}
-- set first rule
g[1] = "S"
g["S"] = g["Exp"] * expect(m.P(-1), "Extra")
for k, v in pairs(labels) do
g[k] = record(k) * sync(v.psync) * v.pcap
end
g = m.P(g)
local function eval(input)
errors = {}
io.write("Input: ", input, "\n")
subject = input
local result, label, suffix = g:match(input)
io.write("Syntactic errors found: " .. #errors, "\n")
if #errors > 0 then
local out = {}
for i, err in ipairs(errors) do
local pos = err.col
local msg = err.msg
table.insert(out, "syntax error: " .. msg .. " (at index " .. pos .. ")")
end
print(table.concat(out, "\n"))
end
io.write("Result = ")
return result
end
print(eval "90-70-(5)+3")
--> 18
print(eval "15+")
--> 2 + 0
print(eval "-2")
--> 0 - 2
print(eval "1+3+-9")
--> 1 + 3 + [0] - 9
print(eval "1+()3+")
--> 1 + ([0]) [+] 3 + [0]
print(eval "8-(2+)-5")
--> 8 - (2 + [0]) - 5
print(eval "()")
print(eval "")
print(eval "1+()+")
print(eval "1+(")
print(eval "3)")
print(eval "11+()3")
--> 1 + ([0]) [+] 3 + [0]
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