I am learning SML, and couldn't figure out why the following textbook code generates an error:
fun recip (x,y) = let val t = x *x + y *y in (x /t, ~y/t) end;
The error is:
Exception- InternalError: asGenReg raised while compiling
This is with Poly/ML 5.7.1.
The code computes the reciprocal of a complex number (x,y). I tried adding ; and parentheses at places to no avail.
Strangely, the following changed (incorrect) definition works without any error.
fun recip (x,y) = let val t = x *x + y *y in (x, ~y/t) end;
The error message is not very informational.
Can someone help explain where the error is and how to fix it?
As the comments @qouify and @mobdnilo pointed out, this error seems to be a bug of the particular version of PolyML in Ubuntu. I reinstalled the PolyML by compiling from source to the latest version (5.9), and the error is gone.