All Questions
Tagged with macros metaprogramming
188
questions
43
votes
1
answer
13k
views
What does the tt metavariable type mean in Rust macros?
I'm reading a book about Rust, and start playing with Rust macros. All metavariable types are explained there and have examples, except the last one – tt. According to the book, it is a “a single ...
- 3,489
31
votes
8
answers
36k
views
How can I simulate macros in JavaScript?
I know that JavaScript doesn't support macros (Lisp-style ones) but I was wondering if anyone had a solution to maybe simulate macros? I Googled it, and one of the solutions suggested using eval(), ...
- 3,768
22
votes
1
answer
2k
views
Generating Clojure code with macro containing type hints
I'm trying to generate some Clojure code with type hints, however the type hints seem to disappear whenever I build some code (they also don't function when the code is compiled)
e.g.
`(let [^...
- 106k
20
votes
3
answers
2k
views
Is there any Template Haskell tutorial for someone who doesn't know Lisp?
I wanted to learn Template Haskell but all tutorials I find either assume that you learned lisp and know what lisp macros are, or that you know some cs theory jargon - things as splices, ...
- 13.8k
16
votes
1
answer
6k
views
Scala macros, where are they used?
I just noticed that Scala has macros, but I have never seen any code that uses them. They also seem quite different from C preprocessor macros and the like. Reading through the overview of macros, it ...
- 6,442
15
votes
4
answers
3k
views
F# Type Providers vs. Lisp macros
I've been reading about F# 3.0 type providers (e.g. here) and it seems that they are based on a kind of compile-time code generation. In that respect I was wondering how they compare against Lisp ...
- 26.6k
13
votes
2
answers
1k
views
Metaprogramming C/C++ using the preprocessor
So I have this huge tree that is basically a big switch/case with string keys and different function calls on one common object depending on the key and one piece of metadata.
Every entry basically ...
- 16.8k
12
votes
5
answers
13k
views
C/C++ macro to repeat code
is there any way to repeat a C code N times with a macro? Also N is a macro.
For example if I have this macros:
#define N 5
#define COODE "nop\n\t"
#define REPEAT [...]
When I call repeat the ...
- 886
10
votes
3
answers
1k
views
How can I avoid repeating myself when creating a C++ enum and a dependent data structure? [duplicate]
Possible Duplicate:
Enum to string : return the enum integer value if invalid / not found
In brief, the (working) definition code that I have is something like this:
enum Gadget
{
First,
...
- 2,013
9
votes
2
answers
2k
views
Quote-unquote idiom in Julia & concatenating Expr objects
I'd like to write a simple macro that shows the names & values of variables. In Common Lisp it would be
(defmacro dprint (&rest vars)
`(progn
,@(loop for v in vars
collect `(...
- 1,844
9
votes
2
answers
3k
views
Elixir macros and bind_quoted
I have a macro that defines a module like so.
defmodule Bar do
def bar do
IO.puts "I am #{inspect __MODULE__}"
end
end
defmodule MacroFun do
defmacro define_module(name) do
quote do
...
- 856
7
votes
6
answers
2k
views
How can one make a 'passthru' function in C++ using macros or metaprogramming?
So I have a series of global functions, say:
foo_f1(int a, int b, char *c);
foo_f2(int a);
foo_f3(char *a);
I want to make a C++ wrapper around these, something like:
MyFoo::f1(int a, int b, char* ...
- 616
7
votes
1
answer
2k
views
Elixir: use macro in the body of same module that defined it
This is common elixir:
defmodule Fizz do
defmacro asdf, do: IO.puts("asdf")
end
defmodule Buzz do
require Fizz
Fizz.asdf
end
However, although you can reference macros in the same context ...
- 7,685
6
votes
5
answers
566
views
Lisp / Clojure: Is it a good idea to write function generating macros?
This question asks to create a Clojure macro to generate several functions. We figured out a way to do this but were stuck with the question of "Is this a good idea?".
My initial reaction is not ...
- 7,976
6
votes
6
answers
4k
views
C++ macro/metaprogram to determine number of members at compile time
I am working on an application with a message based / asynchronous agent-like architecture.
There will be a few dozen distinct message types, each represented by C++ types.
class message_a
{
long ...
- 2,146
6
votes
1
answer
231
views
Non-recursive symbol-macrolet
I'd like to expand all symbols x in a certain fragment into (value x). E.g.
(lambda ()
(* x x))
should become
(lambda ()
(* (value x) (value x)))
A simple use of symbol-macrolet wouldn't work, ...
- 113k
6
votes
3
answers
962
views
How can I print a variable name and its value without typing the name twice?
When you are debugging, it's very useful to do this:
var = calc()
print("var:", var)
Is there any language where this is easy to do? In C and C++ you can use the stringify macro operator # and in ...
- 5,079
6
votes
1
answer
202
views
How to get the literal value of a TemplateHaskell named variable
If I have a Name in TemplateHaskell and want to find out the value of the variable that it names, provided that the variable is declared as a literal, can this be done?
var = "foo"
-- Can `contentsOf`...
- 26.1k
6
votes
1
answer
780
views
Nested macro iteration with C preprocessor
With the C preprocessor you can have some kind of high-order macros. Something like this:
#define ABC(f) f(a) f(b) f(c)
#define XY(f) f(x) f(y)
#define CODE(x) foo_ ## x
ABC(CODE)
#undef CODE
#...
- 83
5
votes
2
answers
1k
views
How to evaluate an expression in nim?
I'm trying to perform the equivalent of the eval method from Python in nim.
I was under the impression that parseStmt from the macros package should help me with this, but I'm facing a compilation ...
- 374
5
votes
2
answers
344
views
Is there a relationship between untyped/typed code quotations in F# and macro hygiene?
I wonder if there is a relationship between untyped/typed code quotations in F# and the hygiene of macro systems. Do they solve the same issues in their respective languages or are they separate ...
- 28.2k
5
votes
6
answers
5k
views
Using C++ Macros To Check For Variable Existence
I am creating a logging facility for my library, and have made some nice macros such as:
#define DEBUG myDebuggingClass(__FILE__, __FUNCTION__, __LINE__)
#define WARING myWarningClass(__FILE__, ...
- 6,168
5
votes
1
answer
524
views
Is there an equivalent of Julia's metaprogramming and macros for JavaScript and TypeScript?
I'm used to Julia macros (metaprogramming), that are a quite handy way of generating flexible code.
https://docs.julialang.org/en/v1/manual/metaprogramming/
Is there an equivalent for JavaScript or ...
- 155
5
votes
1
answer
1k
views
scope of expressions and variables in Julia macro in modules
For some reason, I had to put quote...end block in the macro and ex is generated programmatically. This code works.
macro addsum_out()
quote
ex = :(x+y)
sum(eval(ex))
end
end
x = [1 1 1]
...
- 846
5
votes
1
answer
333
views
Term expansion for a list of terms
Say I want to have a number of rules that all follow the same pattern. I have ran into this situation when I want to avoid non-deterministic behavior by explicitly listing all possible first arguments....
user1812457
5
votes
1
answer
619
views
error: "struct" expression not at top level
function check(str,arg;type=DataType,max=nothing,min=nothing,description="")
@argcheck typeof(arg)==type
@argcheck arg>min
@argcheck arg<max
@argcheck typeof(...
- 653
5
votes
3
answers
2k
views
How could my code tell a compile-time constant versus a variable?
Here's my problem. I have a BINARY_FLAG macro:
#define BINARY_FLAG( n ) ( static_cast<DWORD>( 1 << ( n ) ) )
Which can be used either like this ("constant" scenario):
static const ...
- 169k
5
votes
1
answer
705
views
Why does macro hygiene not prevent collisions between multiple const definitions?
I thought "hygiene" would prevent collisions between Xs defined within my macro m! but that turned out not to be the case. What am I misunderstanding?
macro_rules! m {
($e:expr) => {
...
- 7,871
5
votes
1
answer
668
views
conditionally implement trait inside macro invocation
I'm looking to create a macro to generate thin wrappers for some basic types, for example, the syntax:
wrapper!(String => Email);
would expand to something roughly like:
struct Email {
inner: ...
- 9,663
5
votes
0
answers
290
views
Java's efficient imperative loop through Scala macros?
Scala macros take well-typed terms as arguments instead of arbitrary AST, so it is not obvious to do certain things with them, in particular, introducing a new binding form.
Let's say I want to have ...
- 5,615
4
votes
1
answer
405
views
How to create a macro that suppresses errors and warnings?
I'd like to redefine or overwrite some functions in Base, without the users noticing about this. I found this trick sometime ago:
original_stderr = STDERR
redirect_stderr()
# code
redirect_stderr(...
- 7,763
4
votes
2
answers
277
views
A group of variadic macros
I would like to have a group of variable number of arguments passed into a macro. I have following macros which is incorrect:
#define M_NARGS(...) M_NARGS_(__VA_ARGS__, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, ...
- 3,358
4
votes
2
answers
557
views
A macro for expanding an arbitrary macro a certain number of times?
I want to write the C macros which takes either an integer literal or something akin to an integer literal, and the name of another macro, and expands that other macro as many times as the value of ...
- 124k
4
votes
5
answers
445
views
Emacs metaprogramming, dynamically define methods
I am trying to define some helper functions to quickly jump to different projects from within emacs. I started by defining a macro as follows
(defmacro project-alias (name path)
`(defun ,name ()
...
- 267
4
votes
2
answers
620
views
Creative/interesting uses for C macros; metaprograming [closed]
I have been looking for interesting and preferably useful C macro/defines examples that wold be a bit more extensive than defining consts or min/max functions. It is my understanding that macros ...
- 2,473
4
votes
1
answer
189
views
Is there a way to convert a function to expressions in Julia?
I am trying to create a macro which is capable of (probably recursively) turn a function into expressions so as to reach the operations applied within that function.
As a visualization:
function ...
- 87
4
votes
1
answer
1k
views
Printing the current line in elixir source code
In elixir we have the Pseudo-variables __MODULE__, __DIR__ et al. In erlang there is also the functionality to get the current line, using an erlang macro.
How do I get the current file line in ...
- 4,556
4
votes
2
answers
592
views
Julia: inject code into function
I would like to inject code into a function. For concreteness, consider a simple simulater:
function simulation(A, x)
for t in 1:1000
z = randn(3)
x = A*x + z
end
end
...
- 733
4
votes
2
answers
619
views
Can Julia macros be used to generate code based on specific function implementation?
I am fairly new to Julia and I am learning about metaprogramming.
I would like to write a macro that receive in input a function and returns another function based on the implementation details of ...
- 41
4
votes
1
answer
95
views
Generate functions at macros expansion time
I would like to generate functions for a class accepting 1 type parameter
case class C[T] (t: T)
depending on the T type parameter.
The functions I would like to generate are derived by the ...
- 419
4
votes
1
answer
341
views
Interpolating an expression into an expression inside of a quote
This question builds off of a previous SO question which was for building expressions from expressions inside of of a macro. However, things got a little trucker when quoting the whole expression. For ...
- 19k
3
votes
3
answers
3k
views
Common Lisp: Passing Symbol to Macro
The purpose of this macro is to create a macro that gives a name to accessing a certain key of an associated list.
(defmacro generate-accessor (key-symbol prefix)
(let ((mac-name
(...
- 311
3
votes
4
answers
623
views
C++ Meta-programming
During development of my project in C++ I have a frequent need of debugging and I usually use this macro to do it
#define DBUG(a) {std::cout << #a << " : " << a << std::endl;};...
- 33
3
votes
5
answers
509
views
Need meta-programming magic to define a mother lode of bit fields in an error-free way
The goal is to control which types of users are allowed to perform which operations at the UI level. This code has been in place for a while; I just want to improve it a bit.
The file which I am ...
- 10.6k
3
votes
1
answer
112
views
Julia create multiple slightly modified versions of a function
I have a function that looks like
function eom!(du, u, p)
@views a, b = u[:,1], u[:,2];
@views da, db = du[:,1], du[:,2];
y = # some stuff involving p and a;
da .= f(a, b, y);
db ...
- 1,502
3
votes
4
answers
361
views
Adding default handle_info in __using__ macro
I'm trying to make a little wrapper around ExIrc, but I have encountered a bit of a problem. __using__ macro appends ast to the beginning of the module and I want to append a function definition to ...
- 2,039
3
votes
2
answers
256
views
Macros iterating over undefined Symbols
When applying a macro multiple times with a another macro, bare Symbols are not inserted into the current context:
(defmacro ty [type]
`(deftype ~type []))
(defmacro empties [& args]
(doseq [...
- 3,120
3
votes
1
answer
200
views
How to “splat” the function arguments for dynamically created function
I am generating some functions in the module:
defmodule M do
funs = [do_it: [:arg1, :arg2]]
Enum.each(funs, fn {name, args} ->
args = Enum.map(args, & {&1, [], Elixir})
def ...
- 120k
3
votes
2
answers
359
views
Why is Elixir Logger composed of Macros?
Had to use Logger in one of my applications today, and remembered that I needed to call require Logger first. So I decided to look at the Logger source code to see why debug, info, error, etc. are ...
- 74.6k
3
votes
2
answers
368
views
How can I invoke a macro with all points in a catersian product of argument sets?
Suppose I have a macro
FOO(a, b)
and I want to invoke this macro with a certain (fixed) set of possible values for a; and a certain fixed set of values for b. Thus, if my set of b values is bar and ...
- 124k