How do I define mutually dependent structures?

Thread View: alt.lang.ml

2 messages

[T] Back to Threads [V] Tree View [G] Group Articles

2 total messages Started by Joel F. Klein Sat, 31 Oct 1992 06:16

Author: Joel F. Klein
Date: Sat, 31 Oct 1992 06:16

18 lines
1288 bytes

Can I create two structures which are mutually dependent?
Here is the sml code that describes what I want to do:

signature asig = <<some signature>>
signature bsig = <<some signature>>
functor aFUN(structure s:bsig):asig = struct <<some structure>> end;
functor bFUN(structure s:asig):bsig = struct <<some structure>> end;
structure ta = aFUN(structure s=tb) and tb = bFUN(structure s=ta);

SML-NJ tells me:
std_in:6.33-6.34 Error: unbound structure tb
std_in:6.63-6.64 Error: unbound structure ta

Sigh.  What advantage is there to using the "and" construct if SML can't  
figure out the mutual recursion?  More importantly, am I doing something  
wrong?

Joel F. Klein, email replies to kleinjf@cs.rose-hulman.edu

Re: How do I define mutually dependent structures?

Author: Stefan Kahrs
Date: Mon, 02 Nov 1992 11:13

29 lines
1578 bytes

In article <1ct8crINN1bt@master.cs.rose-hulman.edu> kleinjf@cs.rose-hulman.edu (Joel F. Klein) writes:

>   Can I create two structures which are mutually dependent?

No.

>   Here is the sml code that describes what I want to do:
>
>   signature asig = <<some signature>>
>   signature bsig = <<some signature>>
>   functor aFUN(structure s:bsig):asig = struct <<some structure>> end;
>   functor bFUN(structure s:asig):bsig = struct <<some structure>> end;
>   structure ta = aFUN(structure s=tb) and tb = bFUN(structure s=ta);
>
>   SML-NJ tells me:
>   std_in:6.33-6.34 Error: unbound structure tb
>   std_in:6.63-6.64 Error: unbound structure ta

...which is absolutely correct.

>   Sigh.  What advantage is there to using the "and" construct if SML can't  
>   figure out the mutual recursion?  More importantly, am I doing something  
>   wrong?

You don't do anything wrong.
There are simply no recursive structure in SML,
the "and" construct for structure bindings is certainly a bit misleading.
--
Stefan Kahrs

Thread Navigation

This is a paginated view of messages in the thread with full content displayed inline.

Messages are displayed in chronological order, with the original post highlighted in green.

Use pagination controls to navigate through all messages in large threads.

Back to All Threads