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Feature Request: Per Iteration Variable #418

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anzhi0708 opened this issue Apr 19, 2023 · 2 comments
Open

Feature Request: Per Iteration Variable #418

anzhi0708 opened this issue Apr 19, 2023 · 2 comments
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enhancement New feature or request

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@anzhi0708
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anzhi0708 commented Apr 19, 2023 •
edited
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In this code snippet, the scope of the iteration variable i is global, and the anonymous function captures the variable by reference instead of by value during each iteration, which is consistent with Python but different from functional languages such as OCaml and Scala. To some extent, this behavior goes against intuition.

mut_arr = ![]
for! 0..<5, i =>
  mut_arr.push! ((x: Int)->i)
print! mut_arr

for! mut_arr, f =>
  print! f
  print! f(233)

print! "i = \{i}"

Output:

[<function <lambda> at 0x102d69b20>, <function <lambda> at 0x102d69bc0>, <function <lambda> at 0x102d69ee0>, <function <lambda> at 0x102d69f80>, <function <lambda> at 0x102d6a020>]
<function <lambda> at 0x102d69b20>
4
<function <lambda> at 0x102d69bc0>
4
<function <lambda> at 0x102d69ee0>
4
<function <lambda> at 0x102d69f80>
4
<function <lambda> at 0x102d6a020>
4
i = 4

Scala 3

import scala.collection.mutable.ArrayBuffer
  var functions = ArrayBuffer[()=>Int]()
  for i <- 1 to 10 do
    functions.append(()=>i)
  println(functions)
  println(functions(0)())
  println(functions(1)())
  println(functions(2)())

Output of Scala

ArrayBuffer(hello_world$package$$$Lambda$1391/0x00000008014a1c00@1f521c69, hello_world$package$$$Lambda$1391/0x00000008014a1c00@2b3abeeb, hello_world$package$$$Lambda$1391/0x00000008014a1c00@3aeb267, hello_world$package$$$Lambda$1391/0x00000008014a1c00@13a9cdae, hello_world$package$$$Lambda$1391/0x00000008014a1c00@1c972ae6, hello_world$package$$$Lambda$1391/0x00000008014a1c00@62a41279, hello_world$package$$$Lambda$1391/0x00000008014a1c00@146fa9c0, hello_world$package$$$Lambda$1391/0x00000008014a1c00@49f6c25e, hello_world$package$$$Lambda$1391/0x00000008014a1c00@6c13019c, hello_world$package$$$Lambda$1391/0x00000008014a1c00@2e66f1bd)
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@anzhi0708 anzhi0708 added the enhancement New feature or request label Apr 19, 2023
@mtshiba
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mtshiba commented Apr 23, 2023 •
edited
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I noticed that de-optimization changes the behavior with for!.

for_! = for!

arr = ![]
for_! 0..<5, i =>
    arr.push!(() -> i)

for! arr, f =>
    print! f, f()
<function <lambda> at 0x000001E1B8A3C720> 0
<function <lambda> at 0x000001E1B8B68540> 1
<function <lambda> at 0x000001E1B8B68680> 2
<function <lambda> at 0x000001E1B8B8B060> 3
<function <lambda> at 0x000001E1B8B8B100> 4

De-optimized, pure procedure for! is defined here.

erg/crates/erg_compiler/lib/std/_erg_control.py

Lines 8 to 10 in 3b9f56f

def for__(iterable, body):
for i in iterable:
body(i)

This is what we wanted, but de-optimized version is much slower.

# iteration with 0..<1000000
❯ hyperfine "cargo r test.er" # optimized (normal) version
Benchmark 1: cargo r test.er
  Time (mean ± σ):      1.981 s ±  0.016 s    [User: 1.493 s, System: 0.158 s]
  Range (min … max):    1.964 s …  2.014 s    10 runs

❯ hyperfine "cargo r test.er" # de-optimized version
Benchmark 1: cargo r test.er
  Time (mean ± σ):      3.168 s ±  0.120 s    [User: 2.562 s, System: 0.255 s]
  Range (min … max):    3.088 s …  3.475 s    10 runs

I will try to see if we can get the desired behavior without performance penalty.

@anzhi0708
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Thanks for your reply! This is what I was looking for :-)

@mtshiba mtshiba reopened this Apr 23, 2023
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