Liquidsoap

Add exceptions to the language

Details

  • Type: New Feature New Feature
  • Status: Open Open
  • Priority: Minor Minor
  • Resolution: Unresolved
  • Affects Version/s: None
  • Fix Version/s: None
  • Component/s: None
  • Labels:
    None

Description

Some of the generic functions operating on lists are restricted to lists of strings. For instance:

_[_] : (string,[(string*string)])->string
list.assoc : (string,[(string*string)])->string
list.hd : ([string])->string
etc.

For the two first, this might just be that association lists should be generalized to be able to contain any elements indexed by strings. But list.hd is clearly a bug.

Notice that this is not the case for all functions operating on lists for instance:

list.length : (['a])->int
list.tl : (['a])->['a]

Activity

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David Baelde added a comment -
This isn't a bug but a long-known limitation, because we don't have exceptions. For example, list.hd() can't issue an error when the list is empty, so it returns a default element, the empty string. Coming up with default elements for arbitrary types would be more complex and probably unmanageable for users. We should close this ticket, or rename it to "add exceptions to the language".
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David Baelde added a comment - This isn't a bug but a long-known limitation, because we don't have exceptions. For example, list.hd() can't issue an error when the list is empty, so it returns a default element, the empty string. Coming up with default elements for arbitrary types would be more complex and probably unmanageable for users. We should close this ticket, or rename it to "add exceptions to the language".
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David Baelde added a comment -
Also, for the record: the problem with adding exceptions to the language is that any piece of OCaml code that calls (or evaluates) a piece of script has to handle the case where it fails with an exception.
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David Baelde added a comment - Also, for the record: the problem with adding exceptions to the language is that any piece of OCaml code that calls (or evaluates) a piece of script has to handle the case where it fails with an exception.
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Romain Beauxis added a comment -
I think that using ocaml exceptions to implement liquidsoap's exceptions does not seem like a good idea. Could it be possible to have our own system? Of course, we would probably need to use ocaml's exception but I'd rather see some global catcher implemented somewhere in the core of the language than a per-operator exception handling...
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Romain Beauxis added a comment - I think that using ocaml exceptions to implement liquidsoap's exceptions does not seem like a good idea. Could it be possible to have our own system? Of course, we would probably need to use ocaml's exception but I'd rather see some global catcher implemented somewhere in the core of the language than a per-operator exception handling...
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Romain Beauxis added a comment -
By the way, speaking of lists and default value in case of error, I've always wondered what happens when list.nth should return an error:

% liquidsoap -h list.nth
*** One entry in scripting values:
Get the n-th element of a list (the first element is at position 0).
Category: List
Type: (['a],int)->'a

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Romain Beauxis added a comment - By the way, speaking of lists and default value in case of error, I've always wondered what happens when list.nth should return an error: % liquidsoap -h list.nth *** One entry in scripting values: Get the n-th element of a list (the first element is at position 0). Category: List Type: (['a],int)->'a
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David Baelde added a comment -
Nice catch, this is a bug, or at least a very bad design of list.nth(): it raises Failure "nth" when the index is too large.
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David Baelde added a comment - Nice catch, this is a bug, or at least a very bad design of list.nth(): it raises Failure "nth" when the index is too large.

People

  • Assignee:
    Unassigned
    Reporter:
    Samuel Mimram
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Dates

  • Created:
    Updated: