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Added alternate function, removed relevant code from main; also started working on escape characters

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This commit is contained in:
Aadhavan Srinivasan
2024-10-27 15:30:33 -04:00
parent cda0dfb0cc
commit ae219f763a
2 changed files with 31 additions and 16 deletions
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29
main.go
View File

@@ -54,7 +54,7 @@ func shuntingYard(re string) string {
outQueue := make([]rune, 0) // Output queue
// Actual algorithm
for _, c := range re_postfix {
for i := 0; i < len(re_postfix); i++ {
/* Two cases:
1. Current character is alphanumeric - send to output queue
2. Current character is operator - do the following:
@@ -65,9 +65,19 @@ func shuntingYard(re string) string {
3. If current character is '(', push to opStack
4. If current character is ')', pop from opStack (and append to outQueue) until '(' is found. Discard parantheses.
*/
c := re_postfix[i]
if isAlphaNum(c) {
outQueue = append(outQueue, c)
continue
}
// Escape character - NOT IMPLEMENTED YET - DO NOT USE
// if c == '\\' { // Escape character - next character is treated as alphanum
// if i == len(re_postfix)-1 { // End of string - panic, because backslash is an escape character (something needs to come after it)
// panic("ERROR: Backslash with no escape character.")
// }
// outQueue = append(outQueue, re_postfix[i+1])
// }
if isOperator(c) {
if len(opStack) == 0 {
opStack = append(opStack, c)
@@ -146,21 +156,8 @@ func thompson(re string) *State {
case '|':
s1 := mustPop(&nfa)
s2 := mustPop(&nfa)
s3 := State{}
s3.transitions = make(map[int][]*State)
s3.output = append(s3.output, s1.output...)
s3.output = append(s3.output, s2.output...)
// Unique append is used here (and elsewhere) to ensure that,
// for any given transition, a state can only be mentioned once.
// For example, given the transition 'a', the state 's1' can only be mentioned once.
// This would lead to multiple instances of the same set of match indices, since both
// 's1' states would be considered to match.
s3.transitions[s1.content] = unique_append(s3.transitions[s1.content], s1)
s3.transitions[s2.content] = unique_append(s3.transitions[s2.content], s2)
s3.content = EPSILON
s3.isEmpty = true
nfa = append(nfa, &s3)
s3 := alternate(s1, s2)
nfa = append(nfa, s3)
}
}
if len(nfa) != 1 {

18
nfa.go
View File

@@ -74,3 +74,21 @@ func kleene(s1 State) *State {
toReturn.transitions[s1.content] = unique_append(toReturn.transitions[s1.content], &s1)
return toReturn
}
func alternate(s1 *State, s2 *State) *State {
toReturn := &State{}
toReturn.transitions = make(map[int][]*State)
toReturn.output = append(toReturn.output, s1.output...)
toReturn.output = append(toReturn.output, s2.output...)
// Unique append is used here (and elsewhere) to ensure that,
// for any given transition, a state can only be mentioned once.
// For example, given the transition 'a', the state 's1' can only be mentioned once.
// This would lead to multiple instances of the same set of match indices, since both
// 's1' states would be considered to match.
toReturn.transitions[s1.content] = unique_append(toReturn.transitions[s1.content], s1)
toReturn.transitions[s2.content] = unique_append(toReturn.transitions[s2.content], s2)
toReturn.content = EPSILON
toReturn.isEmpty = true
return toReturn
}