From e649f2d988ce4e7a67aee1236850eb0b95a97d56 Mon Sep 17 00:00:00 2001
From: Boris Kolpackov <boris@codesynthesis.com>
Date: Mon, 14 Dec 2015 10:12:23 +0200
Subject: Add support for variable prepend operator: =+

---
 build/lexer.cxx | 54 +++++++++++++++++++++++++++++++++---------------------
 1 file changed, 33 insertions(+), 21 deletions(-)

(limited to 'build/lexer.cxx')

diff --git a/build/lexer.cxx b/build/lexer.cxx
index 77e803c..0835704 100644
--- a/build/lexer.cxx
+++ b/build/lexer.cxx
@@ -8,6 +8,8 @@ using namespace std;
 
 namespace build
 {
+  typedef token_type type;
+
   token lexer::
   next ()
   {
@@ -47,7 +49,7 @@ namespace build
     uint64_t ln (c.line), cn (c.column);
 
     if (eos (c))
-      return token (token_type::eos, sep, ln, cn);
+      return token (type::eos, sep, ln, cn);
 
     switch (c)
     {
@@ -61,19 +63,19 @@ namespace build
         if (m == lexer_mode::value || m == lexer_mode::pairs)
           mode_.pop ();
 
-        return token (token_type::newline, sep, ln, cn);
+        return token (type::newline, sep, ln, cn);
       }
-    case '{': return token (token_type::lcbrace, sep, ln, cn);
-    case '}': return token (token_type::rcbrace, sep, ln, cn);
-    case '$': return token (token_type::dollar, sep, ln, cn);
-    case '(': return token (token_type::lparen, sep, ln, cn);
-    case ')': return token (token_type::rparen, sep, ln, cn);
+    case '{': return token (type::lcbrace, sep, ln, cn);
+    case '}': return token (type::rcbrace, sep, ln, cn);
+    case '$': return token (type::dollar, sep, ln, cn);
+    case '(': return token (type::lparen, sep, ln, cn);
+    case ')': return token (type::rparen, sep, ln, cn);
     }
 
     // Handle pair separator.
     //
     if (m == lexer_mode::pairs && c == pair_separator_)
-      return token (token_type::pair_separator, sep, ln, cn);
+      return token (type::pair_separator, sep, ln, cn);
 
     // The following characters are not treated as special in the
     // value or pairs mode.
@@ -85,14 +87,24 @@ namespace build
         // NOTE: remember to update name(), next_eval() if adding new
         // special characters.
         //
-      case ':': return token (token_type::colon, sep, ln, cn);
-      case '=': return token (token_type::equal, sep, ln, cn);
+      case ':': return token (type::colon, sep, ln, cn);
+      case '=':
+        {
+          if (peek () == '+')
+          {
+            get ();
+            return token (type::equal_plus, sep, ln, cn);
+          }
+          else
+            return token (type::equal, sep, ln, cn);
+        }
       case '+':
         {
-          if (get () != '=')
-            fail (c) << "expected = after +";
-
-          return token (token_type::plus_equal, sep, ln, cn);
+          if (peek () == '=')
+          {
+            get ();
+            return token (type::plus_equal, sep, ln, cn);
+          }
         }
       }
     }
@@ -122,14 +134,14 @@ namespace build
       // NOTE: remember to update name() if adding new special characters.
       //
     case '\n': fail (c) << "newline in evaluation context";
-    case '{': return token (token_type::lcbrace, sep, ln, cn);
-    case '}': return token (token_type::rcbrace, sep, ln, cn);
-    case '$': return token (token_type::dollar, sep, ln, cn);
-    case '(': return token (token_type::lparen, sep, ln, cn);
+    case '{': return token (type::lcbrace, sep, ln, cn);
+    case '}': return token (type::rcbrace, sep, ln, cn);
+    case '$': return token (type::dollar, sep, ln, cn);
+    case '(': return token (type::lparen, sep, ln, cn);
     case ')':
       {
         mode_.pop (); // Expire eval mode.
-        return token (token_type::rparen, sep, ln, cn);
+        return token (type::rparen, sep, ln, cn);
       }
     }
 
@@ -151,8 +163,8 @@ namespace build
 
     switch (c)
     {
-    case '$': return token (token_type::dollar, false, ln, cn);
-    case '(': return token (token_type::lparen, false, ln, cn);
+    case '$': return token (type::dollar, false, ln, cn);
+    case '(': return token (type::lparen, false, ln, cn);
     }
 
     // Otherwise it is a name.
-- 
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