Add support for lexing and parsing name pairs

We will need it for the buildspec and also if/when we support map
variable types.

1 files changed, 21 insertions, 9 deletions

diff --git a/build/lexer b/build/lexer
index d6817f2..787ba72 100644
--- a/build/lexer
+++ b/build/lexer
@@ -15,11 +15,29 @@
 
 namespace build
 {
+  // Context-dependent lexing mode. In the value mode we don't treat
+  // certain characters (e.g., +, =) as special so that we can use
+  // them in the variable values, e.g., 'foo = g++'. In contrast,
+  // in the variable mode, we restrict certain character (e.g., /)
+  // from appearing in the name. The pairs mode is just like value
+  // except that we split names separated by '='. The pairs mode must
+  // be set manually.
+  //
+  enum class lexer_mode {normal, value, variable, pairs};
+
   class lexer
   {
   public:
     lexer (std::istream& is, const std::string& name): is_ (is), fail (name) {}
 
+    // Note: sets mode for the next token.
+    //
+    void
+    mode (lexer_mode m) {next_mode_ = m;}
+
+    lexer_mode
+    mode () const {return mode_;}
+
     // Scanner.
     //
     token
@@ -108,15 +126,9 @@ namespace build
     xchar buf_ {0, 0, 0};
 
     bool eos_ {false};
-
-    // Context-dependent lexing mode. In the value mode we don't treat
-    // certain characters (e.g., +, =) as special so that we can use
-    // them in the variable values, e.g., 'foo = g++'. In contrast,
-    // in the variable mode, we restrict certain character (e.g., /)
-    // from appearing in the name.
-    //
-    enum class mode {normal, value, variable};
-    mode mode_ {mode::normal};
+    lexer_mode mode_ {lexer_mode::normal};
+    lexer_mode next_mode_; // Mode to switch to for the next token.
+    lexer_mode prev_mode_; // Mode to return to after this mode expires.
   };
 }