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+<b>P</b>ump is <b>U</b>seful for <b>M</b>eta <b>P</b>rogramming.
+
+# The Problem
+
+Template and macro libraries often need to define many classes, functions, or
+macros that vary only (or almost only) in the number of arguments they take.
+It's a lot of repetitive, mechanical, and error-prone work.
+
+Variadic templates and variadic macros can alleviate the problem. However, while
+both are being considered by the C++ committee, neither is in the standard yet
+or widely supported by compilers. Thus they are often not a good choice,
+especially when your code needs to be portable. And their capabilities are still
+limited.
+
+As a result, authors of such libraries often have to write scripts to generate
+their implementation. However, our experience is that it's tedious to write such
+scripts, which tend to reflect the structure of the generated code poorly and
+are often hard to read and edit. For example, a small change needed in the
+generated code may require some non-intuitive, non-trivial changes in the
+script. This is especially painful when experimenting with the code.
+
+# Our Solution
+
+Pump (for Pump is Useful for Meta Programming, Pretty Useful for Meta
+Programming, or Practical Utility for Meta Programming, whichever you prefer) is
+a simple meta-programming tool for C++. The idea is that a programmer writes a
+`foo.pump` file which contains C++ code plus meta code that manipulates the C++
+code. The meta code can handle iterations over a range, nested iterations, local
+meta variable definitions, simple arithmetic, and conditional expressions. You
+can view it as a small Domain-Specific Language. The meta language is designed
+to be non-intrusive (s.t. it won't confuse Emacs' C++ mode, for example) and
+concise, making Pump code intuitive and easy to maintain.
+
+## Highlights
+
+*   The implementation is in a single Python script and thus ultra portable: no
+    build or installation is needed and it works cross platforms.
+*   Pump tries to be smart with respect to
+    [Google's style guide](https://github.com/google/styleguide): it breaks long
+    lines (easy to have when they are generated) at acceptable places to fit
+    within 80 columns and indent the continuation lines correctly.
+*   The format is human-readable and more concise than XML.
+*   The format works relatively well with Emacs' C++ mode.
+
+## Examples
+
+The following Pump code (where meta keywords start with `$`, `[[` and `]]` are
+meta brackets, and `$$` starts a meta comment that ends with the line):
+
+```
+$var n = 3     $$ Defines a meta variable n.
+$range i 0..n  $$ Declares the range of meta iterator i (inclusive).
+$for i [[
+               $$ Meta loop.
+// Foo$i does blah for $i-ary predicates.
+$range j 1..i
+template <size_t N $for j [[, typename A$j]]>
+class Foo$i {
+$if i == 0 [[
+  blah a;
+]] $elif i <= 2 [[
+  blah b;
+]] $else [[
+  blah c;
+]]
+};
+
+]]
+```
+
+will be translated by the Pump compiler to:
+
+```cpp
+// Foo0 does blah for 0-ary predicates.
+template <size_t N>
+class Foo0 {
+  blah a;
+};
+
+// Foo1 does blah for 1-ary predicates.
+template <size_t N, typename A1>
+class Foo1 {
+  blah b;
+};
+
+// Foo2 does blah for 2-ary predicates.
+template <size_t N, typename A1, typename A2>
+class Foo2 {
+  blah b;
+};
+
+// Foo3 does blah for 3-ary predicates.
+template <size_t N, typename A1, typename A2, typename A3>
+class Foo3 {
+  blah c;
+};
+```
+
+In another example,
+
+```
+$range i 1..n
+Func($for i + [[a$i]]);
+$$ The text between i and [[ is the separator between iterations.
+```
+
+will generate one of the following lines (without the comments), depending on
+the value of `n`:
+
+```cpp
+Func();              // If n is 0.
+Func(a1);            // If n is 1.
+Func(a1 + a2);       // If n is 2.
+Func(a1 + a2 + a3);  // If n is 3.
+// And so on...
+```
+
+## Constructs
+
+We support the following meta programming constructs:
+
+| `$var id = exp`                  | Defines a named constant value. `$id` is |
+:                                  : valid util the end of the current meta   :
+:                                  : lexical block.                           :
+| :------------------------------- | :--------------------------------------- |
+| `$range id exp..exp`             | Sets the range of an iteration variable, |
+:                                  : which can be reused in multiple loops    :
+:                                  : later.                                   :
+| `$for id sep [[ code ]]`         | Iteration. The range of `id` must have   |
+:                                  : been defined earlier. `$id` is valid in  :
+:                                  : `code`.                                  :
+| `$($)`                           | Generates a single `$` character.        |
+| `$id`                            | Value of the named constant or iteration |
+:                                  : variable.                                :
+| `$(exp)`                         | Value of the expression.                 |
+| `$if exp [[ code ]] else_branch` | Conditional.                             |
+| `[[ code ]]`                     | Meta lexical block.                      |
+| `cpp_code`                       | Raw C++ code.                            |
+| `$$ comment`                     | Meta comment.                            |
+
+**Note:** To give the user some freedom in formatting the Pump source code, Pump
+ignores a new-line character if it's right after `$for foo` or next to `[[` or
+`]]`. Without this rule you'll often be forced to write very long lines to get
+the desired output. Therefore sometimes you may need to insert an extra new-line
+in such places for a new-line to show up in your output.
+
+## Grammar
+
+```ebnf
+code ::= atomic_code*
+atomic_code ::= $var id = exp
+    | $var id = [[ code ]]
+    | $range id exp..exp
+    | $for id sep [[ code ]]
+    | $($)
+    | $id
+    | $(exp)
+    | $if exp [[ code ]] else_branch
+    | [[ code ]]
+    | cpp_code
+sep ::= cpp_code | empty_string
+else_branch ::= $else [[ code ]]
+    | $elif exp [[ code ]] else_branch
+    | empty_string
+exp ::= simple_expression_in_Python_syntax
+```
+
+## Code
+
+You can find the source code of Pump in [scripts/pump.py](../scripts/pump.py).
+It is still very unpolished and lacks automated tests, although it has been
+successfully used many times. If you find a chance to use it in your project,
+please let us know what you think! We also welcome help on improving Pump.
+
+## Real Examples
+
+You can find real-world applications of Pump in
+[Google Test](https://github.com/google/googletest/tree/master/googletest) and
+[Google Mock](https://github.com/google/googletest/tree/master/googlemock). The
+source file `foo.h.pump` generates `foo.h`.
+
+## Tips
+
+*   If a meta variable is followed by a letter or digit, you can separate them
+    using `[[]]`, which inserts an empty string. For example `Foo$j[[]]Helper`
+    generate `Foo1Helper` when `j` is 1.
+*   To avoid extra-long Pump source lines, you can break a line anywhere you
+    want by inserting `[[]]` followed by a new line. Since any new-line
+    character next to `[[` or `]]` is ignored, the generated code won't contain
+    this new line.