feat(lexer): Scan dot

src/lexer/Error.kt

@@ -0,0 +1,5 @@
+package lexer
+
+class Error(message: String, position: LexerPosition) : Exception("""
+    Error at ${position.line}:${position.column}: $message
+""".trimIndent())

src/lexer/Lexer.kt

@@ -1,11 +1,44 @@
 package lexer
 
-class Lexer {
-    fun scan(source: String): List<Token> {
-        if (source.isEmpty()) {
-            return listOf(Token(TokenType.EOF, LexerPosition(1, 1, 0)))
+import java.util.LinkedList
+
+class Lexer(private val source: String) {
+    private var tokens: List<Token> = LinkedList()
+    private val position: LexerPosition = LexerPosition(0, 0, 0)
+    private var offset: Int = 0
+
+    fun scan(): List<Token> {
+        while (hasNext()) {
+            val token = scanToken()
+            tokens += token
         }
 
-        return emptyList()
+        tokens += Token(TokenType.EOF, position)
+
+        return tokens
+    }
+
+    private fun scanToken(): Token {
+        val c = peek()
+        val token = when (c) {
+            '.' -> Token(TokenType.DOT, position)
+            else -> throw Error("Unknown symbol: $c", position)
+        }
+
+        offset++
+        position.column++
+        return token
+    }
+
+    private fun hasNext(): Boolean {
+        return offset < source.length
+    }
+
+    private fun peek(): Char {
+        if (!hasNext()) {
+            throw Error("Unexpected end of input", position)
+        }
+
+        return source[offset]
     }
 }

src/lexer/LexerPosition.kt

@@ -1,5 +1,5 @@
 package lexer
 
-class LexerPosition(val line: Int, val column: Int, val length: Int) {
+class LexerPosition(val line: Int, var column: Int, val length: Int) {
     // Do nothing
 }

src/lexer/TokenType.kt

@@ -1,5 +1,7 @@
 package lexer
 
 enum class TokenType {
+    DOT,
+
     EOF
 }