From a3f16968a75e3a9b254b6fac7820fea83debd1e8 Mon Sep 17 00:00:00 2001
From: Zahary Karadjov <zahary@gmail.com>
Date: Fri, 24 Feb 2012 16:24:39 +0200
Subject: [PATCH] helper templates static, eval and emit for easier
 compile-time code evaluation

---
 lib/core/macros.nim | 13 ++++++++++++-
 lib/system.nim      | 14 ++++++++++++++
 web/news.txt        |  8 ++++++++
 3 files changed, 34 insertions(+), 1 deletion(-)

diff --git a/lib/core/macros.nim b/lib/core/macros.nim
index 4d13a076d9..e8a16865e4 100755
--- a/lib/core/macros.nim
+++ b/lib/core/macros.nim
@@ -208,7 +208,18 @@ proc getAst*(macroOrTemplate: expr): expr {.magic: "ExpandToAst".}
   ##
   ##   macro FooMacro() = 
   ##     var ast = getAst(BarTemplate())
-  
+
+template emit*(s: expr): stmt =
+  ## accepts a single sting argument and treats it as nimrod code
+  ## that should be inserted verbatim in the program
+  ## Example:
+  ## 
+  ##   emit("echo " & '"' & "hello world".toUpper & '"')
+  ##
+  block:
+    const evaluated = s
+    eval: result = evaluated.parseStmt
+
 proc expectKind*(n: PNimrodNode, k: TNimrodNodeKind) {.compileTime.} =
   ## checks that `n` is of kind `k`. If this is not the case,
   ## compilation aborts with an error message. This is useful for writing
diff --git a/lib/system.nim b/lib/system.nim
index b75f9022dd..bfaa5eb8fa 100755
--- a/lib/system.nim
+++ b/lib/system.nim
@@ -2213,6 +2213,20 @@ proc shallow*(s: var string) {.noSideEffect, inline.} =
     var s = cast[PGenericSeq](s)
     s.reserved = s.reserved or seqShallowFlag
 
+template static*(e: expr): expr =
+  ## evaluates a given expression `e` at compile-time
+  ## even if it has side effects
+  block:
+    const res = e
+    res
+
+template eval*(blk: stmt): stmt =
+  ## executes a block of code at compile time just as if it was a macro
+  ## optonally, the block can return an AST tree that will replace the 
+  ## eval expression
+  block:
+    macro payload(x: stmt): stmt = blk
+    payload()
 
 when defined(initDebugger):
   initDebugger()
diff --git a/web/news.txt b/web/news.txt
index a171f1068e..fdf3a63ea8 100755
--- a/web/news.txt
+++ b/web/news.txt
@@ -20,6 +20,14 @@ Library Additions
 - Added ``system.shallow`` that can be used to speed up string and sequence
   assignments.
 
+- Added ``system.static`` that can force compile-time evaluation of certain
+  expressions
+
+- Added ``system.eval`` that can execute an anonymous block of code at
+  compile time as if was a macro
+
+- Added ``macros.emit`` that can emit an arbitrary computed string as nimrod
+  code during compilation
 
 2012-02-09 Version 0.8.14 released
 ==================================