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ReStructuredText
224 lines
6.0 KiB
ReStructuredText
===========
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Clang-Repl
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===========
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**Clang-Repl** is an interactive C++ interpreter that allows for incremental
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compilation. It supports interactive programming for C++ in a
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read-evaluate-print-loop (REPL) style. It uses Clang as a library to compile the
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high level programming language into LLVM IR. Then the LLVM IR is executed by
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the LLVM just-in-time (JIT) infrastructure.
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Clang-Repl is suitable for exploratory programming and in places where time
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to insight is important. Clang-Repl is a project inspired by the work in
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`Cling <https://github.com/root-project/cling>`_, a LLVM-based C/C++ interpreter
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developed by the field of high energy physics and used by the scientific data
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analysis framework `ROOT <https://root.cern/>`_. Clang-Repl allows to move parts
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of Cling upstream, making them useful and available to a broader audience.
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Clang-Repl Basic Data Flow
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==========================
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.. image:: ClangRepl_design.png
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:align: center
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:alt: ClangRepl design
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Clang-Repl data flow can be divided into roughly 8 phases:
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1. Clang-Repl controls the input infrastructure by an interactive prompt or by
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an interface allowing the incremental processing of input.
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2. Then it sends the input to the underlying incremental facilities in Clang
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infrastructure.
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3. Clang compiles the input into an AST representation.
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4. When required the AST can be further transformed in order to attach specific
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behavior.
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5. The AST representation is then lowered to LLVM IR.
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6. The LLVM IR is the input format for LLVM’s JIT compilation infrastructure.
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The tool will instruct the JIT to run specified functions, translating them
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into machine code targeting the underlying device architecture (eg. Intel
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x86 or NVPTX).
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7. The LLVM JIT lowers the LLVM IR to machine code.
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8. The machine code is then executed.
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Build Instructions:
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===================
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.. code-block:: console
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$ cd llvm-project
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$ mkdir build
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$ cd build
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$ cmake -DCMAKE_BUILD_TYPE=RelWithDebInfo -DLLVM_ENABLE_PROJECTS=clang -G "Unix Makefiles" ../llvm
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**Note here**, above RelWithDebInfo - Debug / Release
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.. code-block:: console
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cmake --build . --target clang clang-repl -j n
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OR
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cmake --build . --target clang clang-repl
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**Clang-repl** is built under llvm-project/build/bin. Proceed into the directory **llvm-project/build/bin**
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.. code-block:: console
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./clang-repl
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clang-repl>
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Clang-Repl Usage
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================
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**Clang-Repl** is an interactive C++ interpreter that allows for incremental
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compilation. It supports interactive programming for C++ in a
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read-evaluate-print-loop (REPL) style. It uses Clang as a library to compile the
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high level programming language into LLVM IR. Then the LLVM IR is executed by
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the LLVM just-in-time (JIT) infrastructure.
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Basic:
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======
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.. code-block:: text
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clang-repl> #include <iostream>
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clang-repl> int f() { std::cout << "Hello Interpreted World!\n"; return 0; }
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clang-repl> auto r = f();
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// Prints Hello Interpreted World!
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.. code-block:: text
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clang-repl> #include<iostream>
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clang-repl> using namespace std;
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clang-repl> std::cout << "Welcome to CLANG-REPL" << std::endl;
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Welcome to CLANG-REPL
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// Prints Welcome to CLANG-REPL
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Function Definitions and Calls:
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===============================
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.. code-block:: text
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clang-repl> #include <iostream>
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clang-repl> int sum(int a, int b){ return a+b; };
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clang-repl> int c = sum(9,10);
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clang-repl> std::cout << c << std::endl;
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19
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clang-repl>
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Iterative Structures:
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=====================
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.. code-block:: text
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clang-repl> #include <iostream>
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clang-repl> for (int i = 0;i < 3;i++){ std::cout << i << std::endl;}
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0
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1
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2
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clang-repl> while(i < 7){ i++; std::cout << i << std::endl;}
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4
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5
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6
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7
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Classes and Structures:
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=======================
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.. code-block:: text
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clang-repl> #include <iostream>
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clang-repl> class Rectangle {int width, height; public: void set_values (int,int);\
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clang-repl... int area() {return width*height;}};
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clang-repl> void Rectangle::set_values (int x, int y) { width = x;height = y;}
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clang-repl> int main () { Rectangle rect;rect.set_values (3,4);\
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clang-repl... std::cout << "area: " << rect.area() << std::endl;\
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clang-repl... return 0;}
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clang-repl> main();
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area: 12
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clang-repl>
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// Note: This '\' can be used for continuation of the statements in the next line
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Lamdas:
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=======
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.. code-block:: text
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clang-repl> #include <iostream>
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clang-repl> using namespace std;
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clang-repl> auto welcome = []() { std::cout << "Welcome to REPL" << std::endl;};
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clang-repl> welcome();
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Welcome to REPL
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Using Dynamic Library:
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======================
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.. code-block:: text
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clang-repl> %lib print.so
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clang-repl> #include"print.hpp"
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clang-repl> print(9);
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9
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**Generation of dynamic library**
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.. code-block:: text
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// print.cpp
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#include <iostream>
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#include "print.hpp"
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void print(int a)
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{
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std::cout << a << std::endl;
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}
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// print.hpp
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void print (int a);
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// Commands
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clang++-17 -c -o print.o print.cpp
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clang-17 -shared print.o -o print.so
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Comments:
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=========
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.. code-block:: text
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clang-repl> // Comments in Clang-Repl
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clang-repl> /* Comments in Clang-Repl */
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Closure or Termination:
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=======================
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.. code-block:: text
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clang-repl>%quit
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Just like Clang, Clang-Repl can be integrated in existing applications as a library
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(using the clangInterpreter library). This turns your C++ compiler into a service that
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can incrementally consume and execute code. The **Compiler as A Service** (**CaaS**)
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concept helps support advanced use cases such as template instantiations on demand and
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automatic language interoperability. It also helps static languages such as C/C++ become
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apt for data science.
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Related Reading
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===============
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`Cling Transitions to LLVM's Clang-Repl <https://root.cern/blog/cling-in-llvm/>`_
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`Moving (parts of) the Cling REPL in Clang <https://lists.llvm.org/pipermail/llvm-dev/2020-July/143257.html>`_
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`GPU Accelerated Automatic Differentiation With Clad <https://arxiv.org/pdf/2203.06139.pdf>`_
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