(This question regards search/6.)
I was wondering if there is a way -rather than manual tracing- to pause the execution of search/6 every time a new solution for a single variable was found?
I would like to accomplish this to further investigate what is happening during search in constrained models.
For example, if you are trying to solve the classic sudoku problem, and you have written a set of constraints and a print method for your board, it can be useful to print the board after setting the constraints, but before searching, in order to evaluate the strongness of your constraints. However, once search is called to solve the sudoku, you don't really have an overview of the single results being built underneath unless you do a trace.
It would be very useful if something was possible in the likes of:
(this is just an abstract example)
% Let's imagine this is a (very poorly) constrained sudoku board
?- problem(Sudoku),constraint(Sudoku),print(Sudoku).
[[1,3,_,2,_,_,7,4,_],
[_,2,5,_,1,_,_,_,_],
[4,8,_,_,6,_,_,5,_],
[_,_,_,7,8,_,2,1,_],
[5,_,_,_,9,_,3,7,_],
[9,_,_,_,3,_,_,_,5],
[_,4,_,_,_,6,8,9,_],
[_,5,3,_,_,1,4,_,_],
[6,_,_,_,_,_,_,_,_]]
Now for the search:
?- problem(Sudoku),constraint(Sudoku),search_pause(Sudoku,BT),print(Sudoku,BT).
[[1,3,6,2,_,_,7,4,_],
[_,2,5,_,1,_,_,_,_],
[4,8,_,_,6,_,_,5,_],
[_,_,_,7,8,_,2,1,_],
[5,_,_,_,9,_,3,7,_],
[9,_,_,_,3,_,_,_,5],
[_,4,_,_,_,6,8,9,_],
[_,5,3,_,_,1,4,_,_],
[6,_,_,_,_,_,_,_,_]]
Board[1,3] = 6
Backtracks = 1
more ;
Using existing Visualization tools
Have a look at the Visualization Tools Manual. You can get the kind of matrix display you want by adding a viewable_create/2 annotation to your code, and launching a Visualisation Client from TkECLiPSe's Tools-menu.
Using your own instrumented search routine
You can replace the indomain_xxx choice methods in search/6 with a user-defined one where you can print information before and/or after propagation.
If that is not enough, you can replace the whole built-in search/6 with your own, which is not too difficult, see e.g. the ECLiPSe Tutorial chapter on tree search or my answer to this question.
Tracing using data-driven facilities
Using ECLiPSe's data-driven control facilities, you can quite easily display information when certain things happen to your variables. In the simplest case you do something on variable instantiation:
?- suspend(printf("X was instantiated to %w%n",[X]), 1, X->inst),
writeln(start), X=3, writeln(end).
start
X was instantiated to 3
end
Based on this idea, you can write code that allows you to follow labeling and propagation steps even when they happen inside a black-box search routine. See the link for details.
(eolp) works only for "hard" line wraps, and I'd like to be able to check whether I'm at the end of screen line. I'd think that looking at the source code of end-of-visual-line would help, but it didn't: it uses a built-in function vertical-motion, and digging into C sources is not something I'd prefer to do. (Of course, I could save point position, go to end-of-visual-line, compare the point position with the saved one, but is there a better way?)
This would be quite useful, especially that I could hit C-t at the end of visual line and not be surprised;).
There may be a better way, but I think your idea to save point position and compare with point at the end of the visual line is reasonable. Lots of things that behave like pure functions in Emacs actually work by changing state like this and restoring it on exit. The save-excursion special form is designed for this kind of pattern:
(defun end-of-visual-line-p ()
(= (point)
(save-excursion
(end-of-visual-line)
(point))))
Is it possible to make Visual Studio to display tooltips on operators?
The following image demonstrates a tooltip hint for a function, but it does not work for operators.
Operators usually have simple type specs like 'T -> 'T -> 'T, but such hints can be useful for custom ones.
Following Daniel's suggestion, I'm posting a workaround that I've been using for myself.
The workaround is only partially helpful, and I'm still looking for any better ideas.
let (!><) a = ()
let z1 = op_BangGreaterLess 5
This code is fully valid, since an operator expression generates a function with a compiler-generated name. See this MSDN article, section "Overloaded Operator Names" for complete list of operator names.
Good news is that op_BangGreaterLess supports IntelliSense hints and it also supports "Go to Definition" (F12) command of IDE, pointing to an original operator declaration.
Bad news is that IntelliSense does not allow rapid entry of the full operator name (Ctrl+Space), so you have to type the entire name manually.
I'm afraid this is not possible (and even in Visual Studio 2012, I don't get tooltips for operators).
I suppose this could be implemented, but as you say, operators usually have simple types. When using custom operators, these should be probably simple enough so that people can use them without looking at their type (or the associated XML documentation). Otherwise, it might be better to use a named function.
That said, if you're using F# Interactive, then you can easily use that to explore the operator type:
> (!><);;
val it : ('a -> unit) = <fun:clo#2>
If I cannot use F# Interactive, I usually define a simple dummy symbol to get the IntelliSense:
let dummy () = (!><)
Note that I added unit argument to define a function and avoid value restriction error.
I'm new to funcctional programming and have some questions regarding coding style and debugging.
I'm under the impression that one should avoid storing results from funcction calls in a temp variable and then return that variable
e.g.
let someFunc foo =
let result = match foo with
| x -> ...
| y -> ...
result
And instead do it like this (I might be way off?):
let someFunc foo =
match foo with
| x -> ...
| y -> ...
Which works fine from a functionallity perspective, but it makes it way harder to debug.
I have no way to examine the result if the right hand side of -> does some funky stuff.
So how should I deal with this kind of scenarios?
To inspect the middle of a pipeline, I suggest the following workaround:
Put this code at some place:
[<AutoOpen>]
module AutoOpenModule
#if DEBUG
let (|>) value func =
let result = func value
result
#endif
Enable "Step Into Properties and Operators in Managed Code":
https://msdn.microsoft.com/en-us/library/cc667388(v=vs.100).aspx
Now you should be able to step into the pipeline operator.
Either way is acceptable, as you are simply binding to local immutable variable.
There is a catch though. If you using it as part of a recursive loop using tail calls, the one using the temp variable will eliminate the tail call, and hence you will have an increase in stack space.
Being able to see the return value of a function in VS is a long-standing request. Other intermediate expression values too; in F# for example, you often want to inspect the middle of a pipeline, which is hard to do. In the sense that functional programming means "fewer named variables and locals" and "larger expressions", this does have a negative impact on the current generation of debuggers. (On the other hand, with things like less mutability and higher abstraction, hopefully you spend less time in the debugger.)
There are still many ways the debuggers of the future can be improved...
See also
Do some Functional programming constructs reduce Debuggability?
I wouldn't shoot you if you used the temp, but I also wouldn't cramp my style on the off chance that I needed to watch something under debug.
Besides, debugging this sort of thing is much easier with Visual Studio 2010's visual debugger, as you can use breakpoints inside each possible match expression. There is also quick watch and other great features.
For a list of the latest features in the Visual Studio debugger:
http://msdn.microsoft.com/en-us/library/01xdt7cs.aspx
Is it possible to get Visual Studio to do mathematical expression evaluation/reduction?
For example if I type '-0.005 + -0.345' how do I get Visual Studio to reduce that (i.e. replace it with the reduction)? Do I have to write a macro? If so, are there any pre-existing macros to do this type of expression reduction?
Just to be clear, I want to be able to highlight an expression and have it replaced with the reduced result. Many are suggesting the immediate window but I fail to see how that will suffice?
Edit I should point out that this is while editing not running or debugging. The immediate window is of little to no use. I also consider this a language neutral question. I would certainly be interested in seeing alternative macros to the one I had posted.
Edit Going Once... Going Twice... (i.e. any other suggestions before I consider accepting my own answer?)
Thank you for the above answers.
There probably are better ways, but here's a quick and dirty macro that does what I need.
References to the System.Data and System.XML namespaces need to be added.
Highlight the expression you want to evaluate and run the macro (it uses the calculated column in the DataTable to evaluate the expression.) It will replace the expression with the reduced result.
Edit - Updated code below. It worked extremely well for reducing a large number of expressions. As pointed out by others there is the immediate window but this will not work for editing purposes. This macro is a language independent solution for basic expressions "(), +, -, *, /".
Sub Eval()
Dim ts As EnvDTE.TextSelection = DTE.ActiveDocument.Selection
Using dt As New DataTable()
dt.Columns.Add("Expression", GetType(Double), ts.Text)
dt.Rows.Add(dt.NewRow)
ts.Text = CDbl(dt.Rows(0).Item("Expression"))
End Using
End Sub
Visual Studio by default will not do any mathematical expression evaluation / reduction. I'm not sure if you can get support for that via items like ReSharper, but if it is available it will be in an add-in.
Also, it would be helpful to know the language you are working in?
Some languages may be helpful in this area. F# for instance makes it easy to evaluate expressions in the IDE via the interactive window and will display out the result. This could easily be added back into your code but it doesn't appear to be exactly what you're looking for.
Here's an answer: Yes, it is possible using the following steps. (While technically performing what you're asking for, I'm not sure it will be extremely useful. :-)
Set a breakpoint in your program that's likely to get hit when you debug the program.
Then, run your program under the Visual Studio debugger.
When the breakpoint is hit, open the Watch window.
In the Watch window, add a new watch by clicking in the Name column.
Enter your expression '-0.005 + -0.345' (without the quotes) then hit [Enter].
... You should see the Value column get populated with -0.35.
Of course, that isn't in the context of the editor window ... which is, presumably, where you'd want to perform the reduction. So again, not very useful, I imagine. An add-in is the likely way to do that in the editor window.
You could just go to the immediate window and type "?<yourExpression>"