V: Compose functions not work

[alai04]

V version: V 0.1.28 e666209
OS: MacOS

What did you do?
I want to compose 2 functions, as follows:

fn sqr(n int) int {
    return n*n
}

fn double(n int) int {
    return n+n
}

fn compose(f1, f2 fn(int) int) fn(int) int {
    return fn(n int) int {
        return f1(f2(n))
    }
}

fn main() {
    f := compose(sqr, double)
    println(f(5))
}

What did you expect to see?
In golang, It is work and output 100.

What did you see instead?
But in vlang, It compiled failed and report:

==================
                       ^
/private/var/folders/3l/6gbl43kj0jj6gyngz2hbg7c00000gn/T/v/high_order_fn.tmp.c:1202:13: error: implicit declaration of function 'f2' is invalid in C99 [-Werror,-Wimplicit-function-declaration]
                return f1(f2(n));
                          ^
/private/var/folders/3l/6gbl43kj0jj6gyngz2hbg7c00000gn/T/v/high_order_fn.tmp.c:4635:1: warning: control may reach end of non-void function [-Wreturn-type]
}
^
/private/var/folders/3l/6gbl43kj0jj6gyngz2hbg7c00000gn/T/v/high_order_fn.tmp.c:4736:27: warning: incompatible pointer types passing 'array_fixed_byteptr_100' (aka 'byteptr [100]') to parameter of type 'void **' [-Wincompatible-pointer-types]
                int nr_ptrs = backtrace(buffer, 100);
                                        ^~~~~~
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/execinfo.h:35:21: note: passing argument to parameter here
int backtrace(void**,int) __OSX_AVAILABLE_STARTING(__MAC_10_5, __IPHONE_2_0);
...
==================
(Use `v -cg` to print the entire error message)

builder error: 
==================
C error. This should never happen.

[nedpals]

@alai04 Closures aren't implemented yet so the scope is limited inside the anonymous function for now.

[alai04]

Got it

[nedpals]

We will open this issue for now for tracking.

[thearchitect]

I use closures often, so lack of it prevents me from start using the language.

[Larpon]

I use closures often, so lack of it prevents me from start using the language.

@thearchitect
You can make you own closures until they're implemented:

struct Context {
mut:
  v int
}
inc := fn(mut ctx Context) {
  ctx.v++
}
mut c := Context{}
inc(mut c)
println(c.v)

[thearchitect]

I use closures often, so lack of it prevents me from start using the language.

@thearchitect

You can make you own closures until they're implemented:

struct Context {

mut:

  v int

}

inc := fn(mut ctx Context) {

  ctx.v++

}

mut c := Context{}

inc(mut c)

println(c.v)

Thank you for you reply, Larpon!
Closures is a good tool to make code more understandable and readable. The pattern you offered works, but it makes opposite effect. So the language need closures.