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local m = require"lpeglabel"
local re = require"relabel"
local labels = {
{"ExpTermFirst", "expected an expression"},
{"ExpTermOp", "expected a term after the operator"},
{"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 errors, subject
local function expect(patt, labname)
local i = labelindex(labname)
return patt + m.T(i)
end
local num = m.R("09")^1 / tonumber
local op = m.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]
else
error('unknown operation: ' .. tokens[i])
end
end
return result
end
local g = m.P {
"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"),
}
function recorderror(pos, lab)
local line, col = re.calcline(subject, pos)
table.insert(errors, { line = line, col = col, msg = labels[lab][2] })
end
function record (labname)
return (m.Cp() * m.Cc(labelindex(labname))) / recorderror
end
function sync (p)
return (-p * m.P(1))^0
end
function defaultValue (p)
return p or m.Cc(1000)
end
local grec = m.P {
"S",
S = m.Rec(m.V"A", m.V"ErrExpTermFirst", labelindex("ExpTermFirst")), -- default value is 0
A = m.Rec(m.V"Sg", m.V"ErrExpTermOp", labelindex("ExpTermOp")),
Sg = m.Rec(g, m.V"ErrMisClose", labelindex("MisClose")),
ErrExpTermFirst = record("ExpTermFirst") * sync(op + ")") * defaultValue(),
ErrExpTermOp = record("ExpTermOp") * sync(op + ")") * defaultValue(),
ErrMisClose = record("MisClose") * sync(m.P")") * defaultValue(m.P""),
}
local function eval(input)
errors = {}
io.write("Input: ", input, "\n")
subject = input
local result, label, suffix = grec: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")
--> 20
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")
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