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authorSergio Queiroz <sqmedeiros@gmail.com>2016-12-13 13:30:36 -0300
committerSergio Queiroz <sqmedeiros@gmail.com>2016-12-13 13:30:36 -0300
commit1322d612d72ac658f2aa443dca94954b819c0993 (patch)
treec49772f07f6e2904202142105dabe2e19e457599
parent2f1e173c3d7670f802a087cd2c80afc5b0ed23c3 (diff)
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Removing example "recovery.lua"
-rw-r--r--examples/recovery.lua134
1 files changed, 0 insertions, 134 deletions
diff --git a/examples/recovery.lua b/examples/recovery.lua
deleted file mode 100644
index bb17b54..0000000
--- a/examples/recovery.lua
+++ /dev/null
@@ -1,134 +0,0 @@
1local lpeg = require"lpeglabelrec"
2
3local R, S, P, V = lpeg.R, lpeg.S, lpeg.P, lpeg.V
4local C, Cc, Ct, Cmt = lpeg.C, lpeg.Cc, lpeg.Ct, lpeg.Cmt
5local T, Lc = lpeg.T, lpeg.Lc
6
7-- The `labels` table contains the list of labels that we will be using
8-- as well as the corresponding error message for each label, which will
9-- be used in our error reporting later on.
10local labels = {
11 {"NoExp", "no expression found"},
12 {"Extra", "extra characters found after the expression"},
13 {"ExpTerm", "expected a term after the operator"},
14 {"ExpExp", "expected an expression after the parenthesis"},
15 {"MisClose", "missing a closing ')' after the expression"},
16}
17
18-- The `labelindex` function gives us the index of a label in the
19-- `labels` table, which serves as the integer representation of the label.
20-- We need this because LPegLabel requires us to use integers for the labels.
21local function labelindex(labname)
22 for i, elem in ipairs(labels) do
23 if elem[1] == labname then
24 return i
25 end
26 end
27 error("could not find label: " .. labname)
28end
29
30-- The `errors` table will hold the list of errors recorded during parsing
31local errors = {}
32
33-- The `expect` function takes a pattern and a label and returns a pattern
34-- that throws the specified label if the original pattern fails to match.
35-- Before throwing the label, it records the label to be thrown along with
36-- the position of the failure (index in input string) into the `errors` table.
37local function expect(patt, labname)
38 local i = labelindex(labname)
39 function recorderror(input, pos)
40 table.insert(errors, {i, pos})
41 return true
42 end
43 return patt + Cmt("", recorderror) * T(i)
44end
45
46local num = R("09")^1 / tonumber
47local op = S("+-*/")
48
49-- The `compute` function takes an alternating list of numbers and
50-- operators and computes the result of applying the operations
51-- to the numbers in a left to right order (no operator precedence).
52local function compute(tokens)
53 local result = tokens[1]
54 for i = 2, #tokens, 2 do
55 if tokens[i] == '+' then
56 result = result + tokens[i+1]
57 elseif tokens[i] == '-' then
58 result = result - tokens[i+1]
59 elseif tokens[i] == '*' then
60 result = result * tokens[i+1]
61 elseif tokens[i] == '/' then
62 result = result / tokens[i+1]
63 else
64 error('unknown operation: ' .. tokens[i])
65 end
66 end
67 return result
68end
69
70-- Our grammar is a simple arithmetic expression of integers that
71-- does not take operator precedence into account but allows grouping
72-- via parenthesis. We have incorporated some error recovery startegies
73-- to our grammar so that it may resume parsing even after encountering
74-- an error, which allows us to report more errors.
75local g = P {
76 "Exp",
77 Exp = Ct(V"Term" * (C(op) * V"OpRecov")^0) / compute;
78 -- `OpRecov` handles missing terms/operands by returning a dummy (zero).
79 OpRecov = Lc(V"Operand", Cc(0), labelindex("ExpTerm"));
80 Operand = expect(V"Term", "ExpTerm");
81 Term = num + V"Group";
82 -- `Group` handles missing closing parenthesis by simply ignoring it.
83 -- Like all the others, the error is still recorded of course.
84 Group = "(" * V"InnerExp" * Lc(expect(")", "MisClose"), P"", labelindex("MisClose"));
85 -- `InnerExp` handles missing expressions by skipping to the next closing
86 -- parenthesis. A dummy (zero) is returned in place of the expression.
87 InnerExp = Lc(expect(V"Exp", "ExpExp"), (P(1) - ")")^0 * Cc(0), labelindex("ExpExp"));
88}
89
90g = expect(g, "NoExp") * expect(-P(1), "Extra")
91
92-- The `eval` function takes an input string to match against the grammar
93-- we've just defined. If the input string matches, then the result of the
94-- computation is returned, otherwise we return the error messages and
95-- positions of all the failures encountered.
96local function eval(input)
97 local result, label, suffix = g:match(input)
98 if #errors == 0 then
99 return result
100 else
101 local out = {}
102 for i, err in ipairs(errors) do
103 local pos = err[2]
104 local msg = labels[err[1]][2]
105 table.insert(out, "syntax error: " .. msg .. " (at index " .. pos .. ")")
106 end
107 errors = {}
108 return nil, table.concat(out, "\n")
109 end
110end
111
112print(eval "98-76*(54/32)")
113--> 37.125
114
115print(eval "(1+1-1*2/2")
116--> syntax error: missing a closing ')' after the expression (at index 11)
117
118print(eval "(1+)-1*(2/2)")
119--> syntax error: expected a term after the operator (at index 4)
120
121print(eval "(1+1)-1*(/2)")
122--> syntax error: expected an expression after the parenthesis (at index 10)
123
124print(eval "1+(1-(1*2))/2x")
125--> syntax error: extra chracters found after the expression (at index 14)
126
127print(eval "-1+(1-(1*2))/2")
128--> syntax error: no expression found (at index 1)
129
130print(eval "(1+1-1*(2/2+)-():")
131--> syntax error: expected a term after the operator (at index 13)
132--> syntax error: expected an expression after the parenthesis (at index 16)
133--> syntax error: missing a closing ')' after the expression (at index 17)
134--> syntax error: extra characters found after the expression (at index 17)