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programming - Checking the argument of user-defined function with side-effect method


Today, I answered a question of mine that asked two month ago. Please see here


Now I would like to add the argument checking in this function. Then I used a method that Mr.Wizard answered


Requirement for the arguments of Bernstein[n,i,u]



  • n must be a integer like 1,2,3,...;

  • i must be a integer like 1,2,3,...;

  • i should between 0 and n-1.



For instance, the built-in BernsteinBasis gives the warning information as below:


BernsteinBasis[1.2, 2, 3]


BernsteinBasis::intnm: Non-negative machine-sized integer expected at position 1 in BernsteinBasis[1.2,2,3]. >>



BernsteinBasis[1.2, 2.1, 3]



BernsteinBasis::intnm: Non-negative machine-sized integer expected at position 1 in BernsteinBasis[1.2,2.1,3]. >>


BernsteinBasis::intnm: Non-negative machine-sized integer expected at position 2 in BernsteinBasis[1.2,2.1,3]. >>



BernsteinBasis[4, 5, u]


BernsteinBasis::invidx2:Index 5 should be a machine-sized integer between 0 and 4. >>



checkArgs


Attributes[checkArgs] = {HoldAll};

(*check the number of arguments*)
checkArgs [func_[args___]] /; Length@{args} != 3 := 
  Message[func::argrx, func, Length@{args}, 3]

(*check the type of the first arguments*)
checkArgs [func_[a_, b_, c_]] /; ! MatchQ[a, _Integer?NonNegative] := 
  Message[func::intnm, func[a, b, c], 1]

(*check the type of second arguments*)
checkArgs [func_[a_, b_, c_]] /; ! MatchQ[b, _Integer?NonNegative] := 

  Message[func::intnm, func[a, b, c], 2]

checkArgs[func_[a_, b_, c_]] /; ! (0 <= b <= a - 1) := 
  Message[func::invidx, b, 0, a - 1]

(*other valid cases*)
checkArgs[other_] := True

Main implementation


Bernstein::invidx = 

 "The index `1` should be a non-negative machine-sized integer betwwen `2` and `3`.";

 SetAttributes[Bernstein, {Listable, NHoldAll, NumericFunction}]
(*special cases*)

Bernstein[n_, i_, u_]?checkArgs /; i < 0 || i > n := 0

Bernstein[0, 0, u_]?checkArgs := 1

Bernstein[n_, i_, u_?NumericQ]?checkArgs := 

 Binomial[n, i] u^i (1 - u)^(n - i)

(*expansion of the basis of Bernstein*)
Bernstein /: PiecewiseExpand[Bernstein[n_, i_, u_]] := 
 Piecewise[
  {{Binomial[n, i] u^i (1 - u)^(n - i), 0 <= u <= 1}, 
   {0, u > 1 || u < 0}}]

(*the derivatives of the basis of Bernstein*)
Bernstein /: Derivative[0, 0, k_Integer?Positive][Bernstein] := 

 Function[{n, i, u}, 
  D[
   n (Bernstein[n - 1, i - 1, u] - Bernstein[n - 1, i, u]), 
   {u, k - 1}]
 ]

However, it gives the following information.



$RecursionLimit::reclim: Recursion depth of 256 exceeded. >>


$RecursionLimit::reclim: Recursion depth of 256 exceeded. >>



$RecursionLimit::reclim: Recursion depth of 256 exceeded. >>


General::stop: Further output of $RecursionLimit::reclim will be suppressed during this calculation. >>


Bernstein::intnm: Non-negative machine-sized integer expected at position >Bernstein[n_,i_,u_] in 1. >>




Update


Thanks for Mr.Wizard's revision that adding HoldForm in checkArgs to remove the recursion.


In addition, Mr.Wizard given me a hint that ultilizing the Message as a side-effect in the comment


Now I have a reference here


SyntaxInformation[f] = {"ArgumentsPattern" -> {_}};

f[1] := True
f[_] := False
f[x___] /; Message[f::argx, "f", Length@{x}] := Null

Additional, The Toad has a comment as below:



I just remembered why I don't use this in my packages... if you have different messages being thrown based on the form of the input (as I often have), then throwing messages as a side-effect of not matching the form will result in all messages being thrown



However, this demo just for one argument, and when the number of argument greater than 1, I have any idea to deal with Message with side-effect.




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