Added more descriptive comments; throw error if non-greedy operator is used; use new definition for kleene()

compile.go

@@ -112,7 +112,8 @@ func shuntingYard(re string, flags ...ReFlag) ([]postfixNode, error) {
 	// Convert the string to a slice of runes to allow iteration through it
 	re_runes_orig := []rune(re) // This is the rune slice before the first parsing loop (which detects and replaces numeric ranges)
 	re_runes := make([]rune, 0)
-	// Check for numeric range. If we are at the start of a numeric range,
+	// The following checks are performed here:
+	// 	1. 	Check for numeric range. If we are at the start of a numeric range,
 	// 		skip to end and construct the equivalent regex for the range.
 	// 		The reason this is outside the loop below, is that it actually modifies
 	// 		the given regex (we 'cut' the numeric range and 'paste' an equivalent regex).
@@ -122,13 +123,19 @@ func shuntingYard(re string, flags ...ReFlag) ([]postfixNode, error) {
 	// 		complexity.
 	// 		A numeric range has the syntax: <num1-num2>. Ir matches all numbers in this range.
 	//
-	// Also check for non-capturing groups. The LPAREN of a non-capturing group looks like this: '(?:'
+	// 	2. 	Check for non-capturing groups. The LPAREN of a non-capturing group looks like this: '(?:'
 	// 		I take this out, and put in a special character - NONCAPLPAREN_CHAR.
 	//
-	// Another check is made for unescaped brackets - opening brackets are replaced with LBRACKET and closing brackets are replaced with RBRACKET.
+	// 	3. 	Another check is made for unescaped brackets - opening brackets are replaced with
-	// Finally, check for escaped backslashes. Replace these with the BACKSLASH metacharacter. Later, in thompson(),
+	//		LBRACKET and closing brackets are replaced with RBRACKET.
-	// these will be converted back. This avoids confusiuon in detecting whether a character is escaped eg. detecting
+	//
+	// 	4. 	Check for escaped backslashes. Replace these with the BACKSLASH
+	//		metacharacter. Later, in thompson(), these will be converted back. This avoids
+	//		confusion in detecting whether a character is escaped eg. detecting
 	// 		whether '\\[a]' has an escaped opening bracket (it doesn't).
+	//
+	// 	5. 	Check for non-greedy operators. These are not supported at the moment, so an error
+	// 		must be thrown if the user attempts to use a non-greedy operator.
 	for i := 0; i < len(re_runes_orig); i++ {
 		c := re_runes_orig[i]
 		if c == '<' && (i == 0 || (re_runes_orig[i-1] != '\\' && re_runes_orig[i-1] != '?')) {
@@ -172,6 +179,8 @@ func shuntingYard(re string, flags ...ReFlag) ([]postfixNode, error) {
 		} else if c == ']' && (i == 0 || re_runes[len(re_runes)-1] != '\\') {
 			re_runes = append(re_runes, RBRACKET)
 			continue
+		} else if slices.Contains([]rune{'+', '*', '?'}, c) && (i < len(re_runes_orig)-1 && re_runes_orig[i+1] == '?') {
+			return nil, fmt.Errorf("non-greedy operators are not supported")
 		} else {
 			re_runes = append(re_runes, c)
 		}
@@ -1001,15 +1010,24 @@ func thompson(re []postfixNode) (Reg, error) {
 			if err != nil {
 				return Reg{}, fmt.Errorf("error applying kleene star")
 			}
-			stateToAdd := kleene(*s1)
+			stateToAdd, err := kleene(*s1)
+			if err != nil {
+				return Reg{}, err
+			}
 			nfa = append(nfa, stateToAdd)
 		case PLUS: // a+ is equivalent to aa*
 			s1 := mustPop(&nfa)
-			s2 := kleene(*s1)
+			s2, err := kleene(*s1)
+			if err != nil {
+				return Reg{}, err
+			}
 			s1 = concatenate(s1, s2)
 			nfa = append(nfa, s1)
 		case QUESTION: // ab? is equivalent to a(b|)
-			s1 := mustPop(&nfa)
+			s1, err := pop(&nfa)
+			if err != nil {
+				return Reg{}, fmt.Errorf("error applying question operator")
+			}
 			s2 := question(s1)
 			nfa = append(nfa, s2)
 		case PIPE:
@@ -1062,7 +1080,10 @@ func thompson(re []postfixNode) (Reg, error) {
 				stateToAdd = concatenate(stateToAdd, cloneState(state))
 			}
 			if c.endReps == INFINITE_REPS { // Case 3
-				s2 := kleene(*state)
+				s2, err := kleene(*state)
+				if err != nil {
+					return Reg{}, err
+				}
 				stateToAdd = concatenate(stateToAdd, s2)
 			} else { // Case 2
 				for i := c.startReps; i < c.endReps; i++ {

nfa.go

@@ -1,6 +1,7 @@
 package main
 
 import (
+	"fmt"
 	"slices"
 )
 
@@ -268,7 +269,11 @@ func concatenate(s1 *State, s2 *State) *State {
 	return s1
 }
 
-func kleene(s1 State) *State {
+func kleene(s1 State) (*State, error) {
+	if s1.isEmpty && s1.assert != NONE {
+		return nil, fmt.Errorf("previous token is not quantifiable")
+	}
+
 	toReturn := &State{}
 	toReturn.transitions = make(map[int][]*State)
 	toReturn.content = newContents(EPSILON)
@@ -283,7 +288,7 @@ func kleene(s1 State) *State {
 	for _, c := range s1.content {
 		toReturn.transitions[c], _ = unique_append(toReturn.transitions[c], &s1)
 	}
-	return toReturn
+	return toReturn, nil
 }
 
 func alternate(s1 *State, s2 *State) *State {

re_test.go

@@ -465,6 +465,19 @@ var reTests = []struct {
 	{`[\t][\n][\v][\r][\f][\b]`, nil, "\t\n\v\r\f\b", []Group{{0, 6}}},
 	{`.*d`, nil, "abc\nabd", []Group{{4, 7}}},
 	{`(`, nil, "-", nil},
+	{`[\41]`, nil, `!`, []Group{{0, 1}}},
+	{`(?<!abc)(d.f)`, nil, `abcdefdof`, []Group{{6, 9}}},
+	{`[\w-]+`, nil, `laser_beam`, []Group{{0, 10}}},
+	{`M+`, []ReFlag{RE_CASE_INSENSITIVE}, `MMM`, []Group{{0, 3}}},
+	{`m+`, []ReFlag{RE_CASE_INSENSITIVE}, `MMM`, []Group{{0, 3}}},
+	{`[M]+`, []ReFlag{RE_CASE_INSENSITIVE}, `MMM`, []Group{{0, 3}}},
+	{`[m]+`, []ReFlag{RE_CASE_INSENSITIVE}, `MMM`, []Group{{0, 3}}},
+	{`^*`, nil, `-`, nil},
+	{`a[^>]*b`, nil, `a>b`, []Group{}},
+	{`^a*$`, nil, `foo`, []Group{}},
+
+	{`*?`, nil, `-`, nil},
+	{`a*?`, nil, `-`, nil}, // non-greedy operators are not supported
 
 	// Todo - add numeric range tests
 }
@@ -604,7 +617,7 @@ var groupTests = []struct {
 	{`a(?:b|c|d)(.)`, nil, `ace`, []Match{[]Group{{0, 3}, {2, 3}}}},
 	{`a(?:b|c|d)*(.)`, nil, `ace`, []Match{[]Group{{0, 3}, {2, 3}}}},
 	{`a(?:b|c|d)+(.)`, nil, `ace`, []Match{[]Group{{0, 3}, {2, 3}}}},
-	{`a(?:b|(c|e){1,2}?|d)+?(.)`, nil, `ace`, []Match{[]Group{{0, 3}, {1, 2}, {2, 3}}}},
+	{`a(?:b|(c|e){1,2}?|d)+(.)`, nil, `ace`, []Match{[]Group{{0, 3}, {1, 2}, {2, 3}}}},
 	{`(?<!-):(.*)(?<!-):`, nil, `a:bc-:de:f`, []Match{[]Group{{1, 9}, {2, 8}}}},
 	{`(?<!\\):(.*)(?<!\\):`, nil, `a:bc\:de:f`, []Match{[]Group{{1, 9}, {2, 8}}}},
 	{`(?<!\?)'(.*)(?<!\?)'`, nil, `a'bc?'de'f`, []Match{[]Group{{1, 9}, {2, 8}}}},
@@ -612,6 +625,15 @@ var groupTests = []struct {
 	{`([\s]*)([\S]*)([\s]*)`, nil, ` testing!1972`, []Match{[]Group{{0, 13}, {0, 1}, {1, 13}, {13, 13}}, []Group{{13, 13}, {13, 13}, {13, 13}, {13, 13}}}},
 	{`(\s*)(\S*)(\s*)`, nil, ` testing!1972`, []Match{[]Group{{0, 13}, {0, 1}, {1, 13}, {13, 13}}, []Group{{13, 13}, {13, 13}, {13, 13}, {13, 13}}}},
 	{`(([a-z]+):)?([a-z]+)$`, nil, `smil`, []Match{[]Group{{0, 4}, {-1, -1}, {-1, -1}, {0, 4}}}},
+
+	{`(x?)?`, nil, `x`, []Match{[]Group{{0, 1}, {0, 1}}, []Group{{1, 1}, {1, 1}}}},
+	{`"(?:\\"|[^"])*"`, nil, `"\""`, []Match{[]Group{{0, 4}}}},
+
+	{`^((a)c)?(ab)$`, nil, `ab`, []Match{[]Group{{0, 2}, {-1, -1}, {-1, -1}, {0, 2}}}},
+
+	{`^([ab]*)(?=(b)?)c`, nil, `abc`, []Match{[]Group{{0, 3}, {0, 2}}}},
+	{`^([ab]*)(?!(b))c`, nil, `abc`, []Match{[]Group{{0, 3}, {0, 2}}}},
+	{`^([ab]*)(?<!(a))c`, nil, `abc`, []Match{[]Group{{0, 3}, {0, 2}}}},
 }
 
 func TestFindAllMatches(t *testing.T) {