Is there a way to say 64-bit GHC for treating Int as Int32?

Question

I am writing a Haskell code generator for Javascript using GHC as a library. Since Javascript does not have an integer type, and its type Number can only represent integers up to 2⁵³, I ​​represent integers as Numbers, explicitly performing all arithmetic values ​​modulo 2³². This works very well with a 32-bit GHC, but worse with a 64-bit version.

The GHC will gladly force Int64 values ​​to Ints and interpret Int constants as 64-bit values ​​(for example, 0xffffffff turns into 4294967295, rather than -1) and causes all kinds of annoying problems.

The compiler works fine for "normal" web material even on a 64-bit system, provided that the standard libraries are built on a 32-bit machine, but "please do not use large ish digits, OK?". this is not what you want to see in your compiler guide. Some problems (but not all) can be fixed by compiling with -O0, but this (not surprisingly) creates code that is not only slow, but also too large.

So, I need to stop the GHC from assuming that Int and Int64 are equivalent. Is it possible?

Answer 1

This is not possible without using a 32-bit GHC.

The Haskell language standard says that the only thing you know about the Int type is that it has

at least the range [-2 ^ 29 .. 2 ^ 29-1

That way, you can happily trim Int values ​​more than that, and still be a fully compatible version of Haskell 2010!

However, you probably shouldn't do this, and instead look for a 64-bit integer type for JavaScript. The same trick, for example, that GHC supports Int64 on 32-bit machines.

Answer 2

As a rule, "Int" should be used only for things where 2 ^ 29 is large enough, and, moreover, it does not matter. In any other place, use either Integer or one of the Data.Word or Data.Int types (Int8, Int16, etc.). Good examples include most sizes and numbers (but not file sizes, which these days can be significantly larger than 2 ^ 32).

A classic unsuccessful example: Control.Concurrent.threadDelay :: Int -> IO (). The argument is the pause time in uSec. 2 ^ 29 uSec = 8.94784853 minutes (according to Google Calculator). The argument should have been Integer, or at least Word64 (584,554,531 years).

Answer 3

Javascript numbers are represented as doubles, so use Double .