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1319 :: Generate code at runtime

• mora (orginal) [2015-06-13T09:53:00+02:00] view original

  Hi,

  How does the compiler work? Here is what I understand/think right now, please correct me if I'm wrong.

  Let's compile to binary with gcc. There are two kind of operations: which can be run at compile time (magic functions), and which cannot be run at compile time (for example functions call to C code with importc). The statements and expressions with type macro, const, template and when are calculated at compile time, and then the code is converted to a tree (Abstract Syntax Tree), which is compiled to C source. Gcc is called to create the binary.

  Thus the compiler must be able to evaluate the AST as long as it contains simpler magic functions. Is this fast?

  Let's assume that I want to generate code at runtime.

  1. Is it possible to generate an AST at runtime and use the compiler to run this tree? Of course I could use only the so called built-in magic functions. Is this what nimsuggest does? (I couldn't decrypt the code). How fast is this approach?
  2. Is it possible to generate arbitrary code at runtime? For example we don't know an object's fields in advance, because we only learn it at runtime. I guess that we could use the compiler to generate the AST, create the C source, compile it to .so or .dll with gcc and then dynamically load the library.

  Thanks, Peter

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• rku (orginal) [2015-06-13T10:14:04+02:00] view original

  I think you want same thing as compiler does when executing code at compile time. After all compile time for compiler is runtime. Compiler has it's own nim vm. I believe that is used to execute nim code when compiling. However to get this working in your own application you possibly might have to embed most of the compiler in it. What would be not needed is like c/js code generators. Everything else probably needed.

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• Araq (orginal) [2015-06-13T10:28:07+02:00] view original

  compiler/nimeval.nim exports a proc execute*(program: string) which does what you're after: It compiles a Nim program to Nim's AST then to bytecode and then runs the bytecode. compiler/vmops.nim shows how some math and os procs are hooked into the VM so that they can be run even though they end up using importc'ed stuff at runtime.

  You just need to install the compiler Nimble package for this to work, but I'm not aware of anybody who uses it, so ... there be dragons.

  Is it fast? I beat Python's VM in the tests that I did with it. So Nim interprets code faster at compile-time than Python does at runtime. Ymmv of course.

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• mora (orginal) [2015-06-13T13:24:27+02:00] view original

  Thank you, both.

  @Araq I like dragons, so I'll report them when I find one.

  Thanks, Peter

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• andrea (orginal) [2015-06-16T17:17:11+02:00] view original

  I tried to use compiler as a dependency, but it appears that trying to use compiler >= 0.11.2 fails, and the last version published on Nimble is 0.10.3. This version, though, does not work with nim 0.11.2 (which I guess makes sense).

  Would it be possible to get a later version published on nimble?

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• dom96 (orginal) [2015-06-16T21:10:47+02:00] view original

  andrea, make sure you're running the latest Nimble. Adding compiler >= 0.11.3 as a dependency should work fine.

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