From a4bdec34353ad1849f99e6ab0e5f2ad5e74c83b1 Mon Sep 17 00:00:00 2001
From: Sergio Queiroz <sqmedeiros@gmail.com>
Date: Tue, 29 Nov 2016 18:38:55 -0300
Subject: New example shows how to build recovery grammar semiautomatically

---
 examples/expressionRecAut.lua   | 132 ++++++++++++++++++++++++++++++++++++++++
 examples/expressionRecovery.lua |   3 +-
 2 files changed, 134 insertions(+), 1 deletion(-)
 create mode 100644 examples/expressionRecAut.lua

diff --git a/examples/expressionRecAut.lua b/examples/expressionRecAut.lua
new file mode 100644
index 0000000..e098078
--- /dev/null
+++ b/examples/expressionRecAut.lua
@@ -0,0 +1,132 @@
+local m = require"lpeglabelrec"
+local re = require"relabelrec"
+
+local R, S, P, V = m.R, m.S, m.P, m.V
+local C, Cc, Ct, Cmt = m.C, m.Cc, m.Ct, m.Cmt
+local T, Rec = m.T, m.Rec
+
+local num = R("09")^1 / tonumber
+local op = S("+-")
+
+local labels = {}
+local nlabels = 0
+
+local function newError(lab, msg, psync, pcap)
+	nlabels = nlabels + 1
+	psync = psync or m.P(-1)
+	pcap = pcap or m.P""
+	labels[lab] = { id = nlabels, 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, labname)
+  local i = labels[labname].id
+  return patt + T(i)
+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
+
+local g = P {
+	"Exp",
+	Exp = Ct(V"OperandFirst" * (C(op) * V"Operand")^0) / compute,
+	OperandFirst = expect(V"Term", "ExpTermFirst"),
+	Operand = expect(V"Term", "ExpTermOp"),
+	Term = num + V"Group",
+	Group = "(" * 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].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 recg2 = g
+for k, v in pairs(labels) do
+	recg2 = Rec(recg2, record(k) * sync(v.psync) * v.pcap, v.id)
+end
+
+local recg = P {
+	"S",
+	S = Rec(V"A", V"ErrExpTermFirst", labels["ExpTermFirst"].id), -- default value is 0
+	A = Rec(V"Sg", V"ErrExpTermOp", labels["ExpTermOp"].id),
+	Sg = Rec(g, V"ErrMisClose", labels["MisClose"].id),
+	ErrExpTermFirst = record("ExpTermFirst") * sync(op + ")") * defaultValue(),
+	ErrExpTermOp = record("ExpTermOp") * sync(op + ")") * defaultValue(),
+	ErrMisClose = record("MisClose") * sync(P")") * defaultValue(m.P""),
+}
+ 
+                
+local function eval(input)
+	errors = {}
+	subject = input
+  local result, label, suffix = recg2:match(input)
+  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
+	return result	
+end
+
+print(eval "90-70*5")
+--> 20
+
+print(eval "2+")
+--> 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)")
+
diff --git a/examples/expressionRecovery.lua b/examples/expressionRecovery.lua
index a4a3288..c5cbcca 100644
--- a/examples/expressionRecovery.lua
+++ b/examples/expressionRecovery.lua
@@ -91,7 +91,6 @@ local function eval(input)
     for i, err in ipairs(errors) do
       local pos = err.col
       local msg = err.msg
-			print("sub", subject)
       table.insert(out, "syntax error: " .. msg .. " (at index " .. pos .. ")")
     end
     print(table.concat(out, "\n"))
@@ -123,5 +122,7 @@ print(eval "")
 
 print(eval "1+()+")
 
+print(eval "1+(")
+
 print(eval "3)")
 
-- 
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