Implemented numeric constants

src/build/token/Keywords.go

@@ -2,5 +2,6 @@ package token
 
 // Keywords defines the keywords used in the language.
 var Keywords = map[string]bool{
+	"let":    true,
 	"return": true,
 }

src/build/token/List.go

@@ -13,7 +13,7 @@ func (list List) String() string {
 	var last Token
 
 	for _, t := range list {
-		if t.Kind == Identifier && last.Kind == Separator {
+		if last.Kind == Keyword || last.Kind == Separator {
 			builder.WriteByte(' ')
 		}
 

src/build/token/Tokenize.go

@@ -70,6 +70,9 @@ func Tokenize(buffer []byte) List {
 		case ']':
 			tokens = append(tokens, Token{ArrayEnd, i, arrayEndBytes})
 
+		case '=', ':', '+', '-', '*', '/', '<', '>', '!':
+			tokens = append(tokens, Token{Operator, i, buffer[i : i+1]})
+
 		// Separator
 		case ',':
 			tokens = append(tokens, Token{Separator, i, separatorBytes})
@@ -147,3 +150,7 @@ func isNumber(c byte) bool {
 func isNumberStart(c byte) bool {
 	return isNumber(c) || c == '-'
 }
+
+func isOperator(c byte) bool {
+	return c == '=' || c == ':' || c == '+' || c == '-' || c == '*' || c == '/' || c == '<' || c == '>' || c == '!'
+}