1 files changed, 128 insertions, 0 deletions

diff --git a/examples/expRec.lua b/examples/expRec.lua
new file mode 100644
index 0000000..5c5fd7d
--- /dev/null
+++ b/examples/expRec.lua
@@ -0,0 +1,128 @@
+local m = require"lpeglabelrec"
+local re = require"relabelrec"
+
+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")
+