Escape quotes, newlines, tabs

lib/ahem/lexer.rb

       number = source.match(/^\d+(\.\d+)?/)[0]
       @position += number.size
       Token.new(TokenKinds::NUMBER, number.to_f)
-    elsif source.match(/^"(.*)"/)
-      string = source.match(/^"([^"]*)"/)[1]
-      @position += (string.size + 2)
+    elsif source[0] == '"'
+      @position += 1
+      string = String.new
+
+      while !at_end && @source[@position] != '"'
+        if @source[@position] == '\\'
+          if @source[@position + 1] == '"'
+            @position += 1
+          elsif @source[@position + 1] == 'n'
+            @position += 2
+            string << "\n"
+            next
+          elsif @source[@position + 1] == 't'
+            @position += 2
+            string << "\t"
+            next
+          end
+        end
+
+        string << @source[@position]
+        @position += 1
+      end
+
+      if at_end
+        raise 'Unterminated string'
+      elsif @source[@position] == '"'
+        @position += 1
+      end
+
       Token.new(TokenKinds::STRING, string)
     elsif source.match(/^\:([a-z][a-zA-Z0-9_]*)/)
       atom = source.match(/^\:([a-z][a-zA-Z0-9_]*)/)[1]

spec/lexer_spec.rb

       ]
     )
   end
+
+  it 'allows escaping quotes in strings' do
+    expect(Lexer.new('"hello \"world\""').scan_all).to eq(
+      [
+        Token.new(TokenKinds::STRING, 'hello "world"'),
+        Token.new(TokenKinds::EOF),
+      ]
+    )
+  end
+
+  it 'supports newlines and tabs in strings' do
+    expect(Lexer.new('"hello\nworld" "hello\tworld"').scan_all).to eq(
+      [
+        Token.new(TokenKinds::STRING, "hello\nworld"),
+        Token.new(TokenKinds::STRING, "hello\tworld"),
+        Token.new(TokenKinds::EOF),
+      ]
+    )
+  end
 end