Why must named functions be in a separate file in hugs?

Question

In Haskell in 5 steps the factorial function is defined as follows:

let fac n = if n == 0 then 1 else n * fac (n-1)

But for hugs, it says that fac needs to be in fac.h. Can anyone explain why this is the case - missing the ability to define named functions seems like a massive limitation for an interpreter?

Just FYI, GHCi can define functions. I don't see much reason to be using Hugs these days. — Chuck, Mar 30 '10 at 15:26

score 2 · Answer 1 · answered Mar 30 '10 at 10:32

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Hugs misses the ability to define any named functions (recursive or not). It also misses the ability to define data types.

answered Mar 30 '10 at 10:32

sepp2k

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This says that it has the limitation, not why the limitation exists. – Mar 30 '10 at 10:34
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Thanks for the clarification, but I'm still curious why they decided not to provide this feature. – Casebash Mar 30 '10 at 12:02

score 2 · Accepted Answer · answered Mar 30 '10 at 15:37

The basic answer as far as I can tell is that the Hugs interactive toplevel is essentially an expression parser, and function/data definitions are not expressions. Your example actually would work if you made it an expression and wrote let fac n = if n == 0 then 1 else n * fac (n-1) in fac 19. Adding support for this would be a pretty big effort, and apparently the Hugs implementors thought that it was good enough to require function/data definitions to be in files.

Why must named functions be in a separate file in hugs?

2 Answers2