# Remove their transitions
for s in bads do
- for t in s.ins do t.delete
- for t in s.outs do t.delete
+ for t in s.ins.to_a do t.delete
+ for t in s.outs.to_a do t.delete
end
# Keep only the good stuff
# REQUIRE: self is a DFA
fun to_minimal_dfa: Automaton
do
+ assert_valid
+
trim
+ # Graph of known distinct states.
var distincts = new HashMap[State, Set[State]]
for s in states do
distincts[s] = new HashSet[State]
end
- # split accept states
+ # split accept states.
+ # An accept state is distinct with a non accept state.
for s1 in states do
for s2 in states do
if distincts[s1].has(s2) then continue
end
end
+ # Fixed point algorithm.
+ # * Get 2 states s1 and s2 not yet distinguished.
+ # * Get a symbol w.
+ # * If s1.trans(w) and s2.trans(w) are distinguished, then
+ # distinguish s1 and s2.
var changed = true
- var ints = new Array[Int]
+ var ints = new Array[Int] # List of symbols to check
while changed do
changed = false
for s1 in states do for s2 in states do
if distincts[s1].has(s2) then continue
+
+ # The transitions use intervals. Therefore, for the states s1 and s2,
+ # we need to check only the meaningful symbols. They are the `first`
+ # symbol of each interval and the first one after the interval (`last+1`).
ints.clear
+ # Check only `s1`; `s2` will be checked later when s1 and s2 are switched.
for t in s1.outs do
var sym = t.symbol
assert sym != null
ints.add sym.first
var l = sym.last
- if l != null then ints.add l
+ if l != null then ints.add l + 1
end
+
+ # Check each symbol
for i in ints do
var ds1 = s1.trans(i)
var ds2 = s2.trans(i)
- if ds1 == null and ds2 == null then continue
+ if ds1 == ds2 then continue
if ds1 != null and ds2 != null and not distincts[ds1].has(ds2) then continue
distincts[s1].add(s2)
distincts[s2].add(s1)
end
end
+ # We need to unify not-distinguished states.
+ # Just add an epsilon-transition and DFAize the automaton.
for s1 in states do for s2 in states do
if distincts[s1].has(s2) then continue
s1.add_trans(s2, null)
return to_dfa
end
+ # Assert that `self` is a valid automaton or abort
+ fun assert_valid
+ do
+ assert states.has(start)
+ assert states.has_all(accept)
+ for s in states do
+ for t in s.outs do assert states.has(t.to)
+ for t in s.ins do assert states.has(t.from)
+ end
+ assert states.has_all(tags.keys)
+ for t, ss in retrotags do
+ assert states.has_all(ss)
+ end
+ end
+
# Produce a graphvis file for the automaton
fun to_dot(filepath: String)
do
# note: the DFA is not minimized.
fun to_dfa: Automaton
do
+ assert_valid
+
trim
var dfa = new Automaton.empty
end
add "# Lexer generated by nitcc for the grammar {name}\n"
- add "module {name}_lexer is no_warning \"missing-doc\"\n"
+ add "module {name}_lexer is generated, no_warning \"missing-doc\"\n"
add("import nitcc_runtime\n")
var p = parser