From 350a5cc4e3e6c19c2e01d9150b147b696dd13aea Mon Sep 17 00:00:00 2001
From: Tom Willemse <tom@ryuslash.org>
Date: Sat, 7 Aug 2021 21:23:05 -0700
Subject: [PATCH] Chapter 16.4

---
 clox/src/scanner.c | 74 ++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 74 insertions(+)

diff --git a/clox/src/scanner.c b/clox/src/scanner.c
index 15d6484..5e0f4bf 100644
--- a/clox/src/scanner.c
+++ b/clox/src/scanner.c
@@ -18,6 +18,10 @@ void initScanner(const char *source) {
   scanner.line = 1;
 }
 
+static bool isAlpha(char c) {
+  return (c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z') || c == '_';
+}
+
 static bool isDigit(char c) { return c >= '0' && c <= '9'; }
 
 static bool isAtEnd() { return *scanner.current == '\0'; }
@@ -91,6 +95,73 @@ static void skipWhitespace() {
   }
 }
 
+static TokenType checkKeyword(int start, int length, const char *rest,
+                              TokenType type) {
+  if (scanner.current - scanner.start == start + length &&
+      memcmp(scanner.start + start, rest, length) == 0) {
+    return type;
+  }
+
+  return TOKEN_IDENTIFIER;
+}
+
+static TokenType identifierType() {
+  switch (scanner.start[0]) {
+  case 'a':
+    return checkKeyword(1, 2, "nd", TOKEN_AND);
+  case 'c':
+    return checkKeyword(1, 4, "lass", TOKEN_CLASS);
+  case 'e':
+    return checkKeyword(1, 3, "lse", TOKEN_ELSE);
+  case 'f':
+    if (scanner.current - scanner.start > 1) {
+      switch (scanner.start[1]) {
+      case 'a':
+        return checkKeyword(2, 3, "lse", TOKEN_FALSE);
+      case 'o':
+        return checkKeyword(2, 1, "or", TOKEN_FOR);
+      case 'u':
+        return checkKeyword(2, 1, "n", TOKEN_FUN);
+      }
+    }
+    break;
+  case 'i':
+    return checkKeyword(1, 1, "f", TOKEN_IF);
+  case 'n':
+    return checkKeyword(1, 2, "il", TOKEN_NIL);
+  case 'o':
+    return checkKeyword(1, 1, "r", TOKEN_OR);
+  case 'p':
+    return checkKeyword(1, 4, "rint", TOKEN_PRINT);
+  case 'r':
+    return checkKeyword(1, 5, "eturn", TOKEN_RETURN);
+  case 's':
+    return checkKeyword(1, 4, "uper", TOKEN_SUPER);
+  case 't':
+    if (scanner.current - scanner.start > 1) {
+      switch (scanner.start[1]) {
+      case 'h':
+        return checkKeyword(2, 2, "is", TOKEN_THIS);
+      case 'r':
+        return checkKeyword(2, 2, "ue", TOKEN_TRUE);
+      }
+    }
+    break;
+  case 'v':
+    return checkKeyword(1, 2, "ar", TOKEN_VAR);
+  case 'w':
+    return checkKeyword(1, 4, "hile", TOKEN_WHILE);
+  }
+
+  return TOKEN_IDENTIFIER;
+}
+
+static Token identifier() {
+  while (isAlpha(peek()) || isDigit(peek()))
+    advance();
+  return makeToken(identifierType());
+}
+
 static Token number() {
   while (isDigit(peek()))
     advance();
@@ -130,6 +201,9 @@ Token scanToken() {
     return makeToken(TOKEN_EOF);
 
   char c = advance();
+
+  if (isAlpha(c))
+    return identifier();
   if (isDigit(c))
     return number();