1 files changed, 106 insertions, 0 deletions

diff --git a/examples/expectWithRecov.lua b/examples/expectWithRecov.lua
new file mode 100644
index 0000000..8d894c1
--- /dev/null
+++ b/examples/expectWithRecov.lua
@@ -0,0 +1,106 @@
+local lpeg = require"lpeglabel"
+
+local R, S, P, V = lpeg.R, lpeg.S, lpeg.P, lpeg.V
+local C, Cc, Ct, Cmt = lpeg.C, lpeg.Cc, lpeg.Ct, lpeg.Cmt
+local T, Lc = lpeg.T, lpeg.Lc
+
+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 errors = {}
+
+local function expect(patt, labname)
+  local i = labelIndex(labname)
+  function recordError(input, pos)
+    table.insert(errors, {i, pos})
+    return true
+  end
+  return patt + Cmt("", recordError) * T(i)
+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"OpRecov")^0) / compute;
+  OpRecov = Lc(V"Operand", Cc(0), labelIndex("ExpTerm"));
+  Operand = expect(V"Term", "ExpTerm");
+  Term = num + V"Group";
+  Group = "(" * V"InnerExp" * Lc(expect(")", "MisClose"), P"", labelIndex("MisClose"));
+  InnerExp = Lc(expect(V"Exp", "ExpExp"), (P(1) - ")")^0 * Cc(0), labelIndex("ExpExp"));
+}
+
+g = expect(g, "NoExp") * expect(-P(1), "Extra")
+
+local function eval(input)
+  local result, label, suffix = g:match(input)
+  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]
+      out = out .. "syntax error: " .. msg .. " (at index " .. pos .. ")\n"
+    end
+    errors = {}
+    return nil, out
+  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)