Removed some panics with error throwing; changed some comments; removed use of mustPop() in parsing Kleene star - I use pop() and then throw an error if pop() returns an error

compile.go

@@ -344,7 +344,7 @@ func shuntingYard(re string, flags ...ReFlag) ([]postfixNode, error) {
 		}
 
 		if c == '\\' { // Escape character - invert special and non-special characters eg. \( is treated as a literal parentheses, \b is treated as word boundary
-			if i == len(re_postfix)-1 { // End of string - panic, because backslash is an escape character (something needs to come after it)
+			if i == len(re_postfix)-1 { // End of string - throw error, because backslash is an escape character (something needs to come after it)
 				return nil, fmt.Errorf("backslash with no escape character")
 			}
 			i++
@@ -426,7 +426,7 @@ func shuntingYard(re string, flags ...ReFlag) ([]postfixNode, error) {
 				regex += string(re_postfix[i])
 				i++
 			}
-			if len(regex) <= 1 { // Nothing in regex - panic
+			if len(regex) <= 1 { // Nothing in regex - throw error
 				return nil, fmt.Errorf("invalid lookaround. (too short?)")
 			}
 			// 'regex' should now contain the lookaround regex, plus the characters at the start (which indicate pos/neg, ahead/behind)
@@ -660,7 +660,7 @@ func shuntingYard(re string, flags ...ReFlag) ([]postfixNode, error) {
 					endOfRange = false // Reset the flag
 				}
 			}
-			if i == len(re_postfix) { // We have reached the end of the string, so we didn't encounter a closing brakcet. Panic.
+			if i == len(re_postfix) { // We have reached the end of the string, so we didn't encounter a closing brakcet. Throw error.
 				return nil, fmt.Errorf("opening bracket without closing bracket")
 			}
 
@@ -690,7 +690,7 @@ func shuntingYard(re string, flags ...ReFlag) ([]postfixNode, error) {
 
 			startRangeNum, err := strconv.Atoi(string(startRange))
 			if err != nil {
-				panic(err)
+				return nil, fmt.Errorf("invalid numeric range")
 			}
 
 			if re_postfix[i] == '}' { // Case 1 above
@@ -708,7 +708,7 @@ func shuntingYard(re string, flags ...ReFlag) ([]postfixNode, error) {
 					return nil, fmt.Errorf("brace not closed")
 				}
 				if re_postfix[i] != '}' {
-					return nil, fmt.Errorf("invalid numeric specifier")
+					return nil, fmt.Errorf("invalid start range for numeric specifier")
 				}
 				if len(endRange) == 0 { // Case 3 above
 					endRangeNum = INFINITE_REPS
@@ -716,7 +716,7 @@ func shuntingYard(re string, flags ...ReFlag) ([]postfixNode, error) {
 					var err error
 					endRangeNum, err = strconv.Atoi(string(endRange))
 					if err != nil {
-						panic(err)
+						return nil, fmt.Errorf("invalid end range for numeric specifier")
 					}
 				}
 			}
@@ -737,7 +737,7 @@ func shuntingYard(re string, flags ...ReFlag) ([]postfixNode, error) {
 			numOpenParens++
 		}
 		if c == ')' {
-			// Keep popping from opStack until we encounter an opening parantheses or a NONCAPLPAREN_CHAR. Panic if we reach the end of the stack.
+			// Keep popping from opStack until we encounter an opening parantheses or a NONCAPLPAREN_CHAR. Throw error if we reach the end of the stack.
 			var val rune
 			var err error
 			for val, err = peek(opStack); val != '(' && val != NONCAPLPAREN_CHAR; val, err = peek(opStack) {
@@ -951,7 +951,10 @@ func thompson(re []postfixNode) (Reg, error) {
 				nfa = append(nfa, s1)
 			}
 		case KLEENE: // Create a 0-state, concat the popped state after it, concat the 0-state after the popped state
-			s1 := mustPop(&nfa)
+			s1, err := pop(&nfa)
+			if err != nil {
+				return Reg{}, fmt.Errorf("error applying kleene star")
+			}
 			stateToAdd := kleene(*s1)
 			nfa = append(nfa, stateToAdd)
 		case PLUS: // a+ is equivalent to aa*