Updating examples to the new semantics

1 files changed, 100 insertions, 0 deletions

diff --git a/examples/exp.lua b/examples/exp.lua
new file mode 100644
index 0000000..4afe83e
--- /dev/null
+++ b/examples/exp.lua
@@ -0,0 +1,100 @@
+-- Matthew's recovery example 
+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 = lpeg.T
+
+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 errors = {}
+
+local function expect(patt, labname)
+  function recorderror(input, pos)
+    table.insert(errors, {labname, pos})
+    return true
+  end
+  return patt + Cmt("", recorderror) * T(labname)
+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"Operand")^0) / compute;
+  Operand = expect(V"Term", "ExpTerm");
+  Term = num + V"Group";
+  Group = "(" * V"InnerExp" * expect(")", "MisClose");
+  InnerExp = expect(V"Exp", "ExpExp");
+  ExpTerm = Cc(0);
+  MisClose = P"";
+  ExpExp = (P(1) - ")")^0 * Cc(0);
+}
+
+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]]
+      table.insert(out, "syntax error: " .. msg .. " (at index " .. pos .. ")")
+    end
+    errors = {}
+    return nil, table.concat(out, "\n")
+  end
+end
+
+assert(eval "98-76*(54/32)" == 37.125)
+--> 37.125
+
+local e, msg = eval "(1+1-1*2/2"
+assert(e == nil and msg == "syntax error: missing a closing ')' after the expression (at index 11)")
+
+e, msg = eval "(1+)-1*(2/2)"
+assert(e == nil and msg == "syntax error: expected a term after the operator (at index 4)")
+
+e, msg = eval "(1+1)-1*(/2)"
+assert(e == nil and msg == "syntax error: expected an expression after the parenthesis (at index 10)")
+
+e, msg = eval "1+(1-(1*2))/2x"
+assert(e == nil and msg == "syntax error: extra characters found after the expression (at index 14)")
+
+e, msg = eval "-1+(1-(1*2))/2"
+assert(e == nil and msg == "syntax error: no expression found (at index 1)")
+
+e, msg = eval "(1+1-1*(2/2+)-():"
+assert(e == nil and msg == "syntax error: expected a term after the operator (at index 13)\n" ..
+                           "syntax error: expected an expression after the parenthesis (at index 16)\n" ..
+                           "syntax error: missing a closing ')' after the expression (at index 17)\n" ..
+                           "syntax error: extra characters found after the expression (at index 17)")
+