I have a situation where there are multiple possible errors – I want to catch them and convert the result to failure, but allow any other errors to propagate. This is the code I’ve written … is there a better way of doing this? (Context: I’m doing a bit of cleanup to library(rbtrees)) is_rbtree(t(_…

Here’s another way of doing the same thing: is_rbtree(t(_,T)) => catch( catch( catch(rbtree1(T), msg(_,_), fail), error(instantiation_error,_), fail), error(existence_error(matching_r…

I keep wondering how to best deal with errors – what approach works best in general, architecturally speaking, and for Prolog in particular. Essentially, converting to failure shields the caller from the type of error but also might have “failure” more ambiguous. It would be great if we could a di…

How about a helper predicate? like: is_rbtree(t(_,T)) :- catch(rbtree1(T), Err, is_rbtree_error(Err)). is_rbtree_error(msg(_, _)) :- fail. % EDIT: missing !/0, see note below ... is_rbtree_error(Err) :- throw(Err). EDIT: in case the body of the “handler” clause is not deterministic (which f…

[image] grossdan: Essentially, converting to failure shields the caller from the type of error but also might have “failure” more ambiguous. In this particular case, the predicate is_rbtree/1 wraps another predicate that can either fail or throw an exception. So, here it’s reasonable to conve…

[image] oskardrums: How about a helper predicate? Nice! Thank-you.

Thanks. Indeed, i used the question to ask a broader question, although its related – the architecture of failure handing may also suggest the approach – such as whether further hands-offs are made. Dan

I see two issues. One is selecting exceptions you want to handle. If there is a good pattern where unification does the trick, this is fairly ok. If not, you need a more general pattern and you catch too many, so you need to filter on the ones you want to handle and re-throw otherwise. This i…

[image] jan: exception ball. It sort of makes sense but could ball be a typo? EDIT After seeing reply by Jan W. and being attentive to the idea of a ball is thrown, discovered the terminology is noted in the ISO Prolog standard: 7.8.9 The catch and throw (7.8.10) control constructs enab…

The thing you throw is often called the ball :slight_smile:

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Best practice for catch/3 with multiple possible errors?

Help! Predicate

jan October 14, 2021, 9:13am 10

The thing you throw is often called the ball

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Best practice for catch/3 with multiple possible errors?

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