From 0032516676b486b395086b40641a34f2cafeca99 Mon Sep 17 00:00:00 2001
From: Felix Hanley <felix@userspace.com.au>
Date: Sat, 31 Aug 2019 00:30:28 +1000
Subject: Generation of all but unicode tested

---
 lexer.go | 106 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 106 insertions(+)
 create mode 100644 lexer.go

(limited to 'lexer.go')

diff --git a/lexer.go b/lexer.go
new file mode 100644
index 0000000..a8383a9
--- /dev/null
+++ b/lexer.go
@@ -0,0 +1,106 @@
+package brechars
+
+import (
+	"src.userspace.com.au/felix/lexer"
+)
+
+const (
+	_ lexer.TokenType = iota
+	tBREStart
+	tBREEnd
+	tRangeStart
+	tRangeDash
+	tRangeEnd
+	tCharacter
+	tClass
+	tNot
+)
+
+func startState(l *lexer.Lexer) lexer.StateFunc {
+	l.SkipWhitespace()
+	r := l.Next()
+	if r != '[' {
+		return l.Error("expecting [")
+	}
+	l.Emit(tBREStart)
+	return breFirstState
+}
+
+// Handle the first characters of the BRE.
+func breFirstState(l *lexer.Lexer) lexer.StateFunc {
+	switch l.Next() {
+	case '^':
+		l.Emit(tNot)
+		// - or ] After ^ is literal
+		if l.Accept("-]") {
+			l.Emit(tCharacter)
+		}
+		return breState
+	case ']':
+		// Check for empty BRE
+		if l.Peek() == lexer.EOFRune {
+			l.Emit(tBREEnd)
+			return nil
+		}
+		l.Emit(tCharacter)
+		return breState
+	case '-':
+		l.Emit(tCharacter)
+		return breState
+	default:
+		l.Backup()
+		return breState
+	}
+}
+
+func breState(l *lexer.Lexer) lexer.StateFunc {
+	switch r := l.Next(); {
+	case r == ']':
+		l.Emit(tBREEnd)
+		return nil
+	case r == ':':
+		return classState
+	case r == '-':
+		return l.Error("parse error, unexpected '-'")
+	case r == '\\':
+		if l.Accept("ux") {
+			return unicodeState
+		}
+		l.Emit(tCharacter)
+		return breState
+	case r == lexer.EOFRune:
+		return l.Error("parse error, unexpected EOF")
+	default:
+		if l.Peek() == '-' {
+			l.Emit(tRangeStart)
+			l.Accept("-")
+			l.Emit(tRangeDash)
+			if l.Accept("-][^") {
+				return l.Error("parse error, invalid range end")
+			}
+			l.Next()
+			l.Emit(tRangeEnd)
+		} else {
+			l.Emit(tCharacter)
+		}
+		return breState
+	}
+}
+
+func classState(l *lexer.Lexer) lexer.StateFunc {
+	// TODO
+	l.AcceptRun("abcdefghijklmnopqrstuvwxyz")
+	if !l.Accept(":") {
+		return l.Error("parse error, expecting ':'")
+	}
+	l.Emit(tClass)
+	return breState
+}
+
+func unicodeState(l *lexer.Lexer) lexer.StateFunc {
+	// TODO valid code point
+	if n := l.AcceptRun("0123456789abcdef"); n > 0 {
+		l.Emit(tCharacter)
+	}
+	return breState
+}
-- 
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