Is there a defined priority for pattern matching?












4












$begingroup$


If you define a function g, like so:



g[x_?EvenQ] := "even"    

g[x_?NumberQ] := "number"


why will Mathematica always return g[2] == "Even", even though NumberQ[2] == True?



More specifically, is there a defined order in which Mathematica will try to match function cases? Does it evaluate the most specific match first?






pattern-matching expression-test







share|improve this question









New contributor




wgoodall01 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.







$endgroup$












  • $begingroup$
    g[x_NumberQ] means to match arguments with the head NumberQ. What you want is to match arguments such that NumberQ[x] is True, which is g[x_?NumberQ]. Look up PatternTest. (Before you make this correction, make sure to run Clear[g] first.)
    $endgroup$
    – J. M. is computer-less♦
    2 hours ago












  • $begingroup$
    That's right---fixed.
    $endgroup$
    – wgoodall01
    2 hours ago






  • 2




    $begingroup$
    Once you have made this fix, evaluate DownValues[g]; that should give a hint as to which case gets applied first. Generally, it tries to put special cases first before general ones.
    $endgroup$
    – J. M. is computer-less♦
    2 hours ago












  • $begingroup$
    Or just execute ?g to see the order of the definitions.
    $endgroup$
    – Roman
    1 hour ago
















4












$begingroup$


If you define a function g, like so:



g[x_?EvenQ] := "even"    

g[x_?NumberQ] := "number"


why will Mathematica always return g[2] == "Even", even though NumberQ[2] == True?



More specifically, is there a defined order in which Mathematica will try to match function cases? Does it evaluate the most specific match first?






pattern-matching expression-test







share|improve this question









New contributor




wgoodall01 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.







$endgroup$












  • $begingroup$
    g[x_NumberQ] means to match arguments with the head NumberQ. What you want is to match arguments such that NumberQ[x] is True, which is g[x_?NumberQ]. Look up PatternTest. (Before you make this correction, make sure to run Clear[g] first.)
    $endgroup$
    – J. M. is computer-less♦
    2 hours ago












  • $begingroup$
    That's right---fixed.
    $endgroup$
    – wgoodall01
    2 hours ago






  • 2




    $begingroup$
    Once you have made this fix, evaluate DownValues[g]; that should give a hint as to which case gets applied first. Generally, it tries to put special cases first before general ones.
    $endgroup$
    – J. M. is computer-less♦
    2 hours ago












  • $begingroup$
    Or just execute ?g to see the order of the definitions.
    $endgroup$
    – Roman
    1 hour ago














4












4








4





$begingroup$


If you define a function g, like so:



g[x_?EvenQ] := "even"    

g[x_?NumberQ] := "number"


why will Mathematica always return g[2] == "Even", even though NumberQ[2] == True?



More specifically, is there a defined order in which Mathematica will try to match function cases? Does it evaluate the most specific match first?






pattern-matching expression-test







share|improve this question









New contributor




wgoodall01 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.







$endgroup$




If you define a function g, like so:



g[x_?EvenQ] := "even"    

g[x_?NumberQ] := "number"


why will Mathematica always return g[2] == "Even", even though NumberQ[2] == True?



More specifically, is there a defined order in which Mathematica will try to match function cases? Does it evaluate the most specific match first?






pattern-matching expression-test




pattern-matching expression-test






share|improve this question









New contributor




wgoodall01 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.











share|improve this question









New contributor




wgoodall01 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.









share|improve this question




share|improve this question








edited 2 hours ago







wgoodall01













New contributor




wgoodall01 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.









asked 2 hours ago









wgoodall01wgoodall01

1235




1235




New contributor




wgoodall01 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
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New contributor





wgoodall01 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.






wgoodall01 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.












  • $begingroup$
    g[x_NumberQ] means to match arguments with the head NumberQ. What you want is to match arguments such that NumberQ[x] is True, which is g[x_?NumberQ]. Look up PatternTest. (Before you make this correction, make sure to run Clear[g] first.)
    $endgroup$
    – J. M. is computer-less♦
    2 hours ago












  • $begingroup$
    That's right---fixed.
    $endgroup$
    – wgoodall01
    2 hours ago






  • 2




    $begingroup$
    Once you have made this fix, evaluate DownValues[g]; that should give a hint as to which case gets applied first. Generally, it tries to put special cases first before general ones.
    $endgroup$
    – J. M. is computer-less♦
    2 hours ago












  • $begingroup$
    Or just execute ?g to see the order of the definitions.
    $endgroup$
    – Roman
    1 hour ago


















  • $begingroup$
    g[x_NumberQ] means to match arguments with the head NumberQ. What you want is to match arguments such that NumberQ[x] is True, which is g[x_?NumberQ]. Look up PatternTest. (Before you make this correction, make sure to run Clear[g] first.)
    $endgroup$
    – J. M. is computer-less♦
    2 hours ago












  • $begingroup$
    That's right---fixed.
    $endgroup$
    – wgoodall01
    2 hours ago






  • 2




    $begingroup$
    Once you have made this fix, evaluate DownValues[g]; that should give a hint as to which case gets applied first. Generally, it tries to put special cases first before general ones.
    $endgroup$
    – J. M. is computer-less♦
    2 hours ago












  • $begingroup$
    Or just execute ?g to see the order of the definitions.
    $endgroup$
    – Roman
    1 hour ago
















$begingroup$
g[x_NumberQ] means to match arguments with the head NumberQ. What you want is to match arguments such that NumberQ[x] is True, which is g[x_?NumberQ]. Look up PatternTest. (Before you make this correction, make sure to run Clear[g] first.)
$endgroup$
– J. M. is computer-less♦
2 hours ago






$begingroup$
g[x_NumberQ] means to match arguments with the head NumberQ. What you want is to match arguments such that NumberQ[x] is True, which is g[x_?NumberQ]. Look up PatternTest. (Before you make this correction, make sure to run Clear[g] first.)
$endgroup$
– J. M. is computer-less♦
2 hours ago














$begingroup$
That's right---fixed.
$endgroup$
– wgoodall01
2 hours ago




$begingroup$
That's right---fixed.
$endgroup$
– wgoodall01
2 hours ago




2




2




$begingroup$
Once you have made this fix, evaluate DownValues[g]; that should give a hint as to which case gets applied first. Generally, it tries to put special cases first before general ones.
$endgroup$
– J. M. is computer-less♦
2 hours ago






$begingroup$
Once you have made this fix, evaluate DownValues[g]; that should give a hint as to which case gets applied first. Generally, it tries to put special cases first before general ones.
$endgroup$
– J. M. is computer-less♦
2 hours ago














$begingroup$
Or just execute ?g to see the order of the definitions.
$endgroup$
– Roman
1 hour ago




$begingroup$
Or just execute ?g to see the order of the definitions.
$endgroup$
– Roman
1 hour ago










1 Answer
1






active

oldest

votes


















6












$begingroup$

TheOrderingOfDefinitions




  • ... The Wolfram System follows the principle of trying to put more general definitions after more specific ones. This means that special cases of rules are typically tried before more general cases.

  • Although in many practical cases, the Wolfram System can recognize when one rule is more general than another, you should realize that this is not always possible. For example, if two rules both contain complicated /; conditions, it may not be possible to work out which is more general, and, in fact, there may not be a definite ordering. Whenever the appropriate ordering is not clear, the Wolfram System stores rules in the order you give them.




ClearAll[g]

g[x_?EvenQ] := "even"

g[x_?NumberQ] := "number"

g /@ {1, 2}



{"number", "even"}




ClearAll[h]

h[x_?NumberQ] := "number"

h[x_?EvenQ] := "even"

h /@ {1, 2}



{"number", "number"}







share|improve this answer











$endgroup$













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    1 Answer
    1






    active

    oldest

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    1 Answer
    1






    active

    oldest

    votes









    active

    oldest

    votes






    active

    oldest

    votes









    6












    $begingroup$

    TheOrderingOfDefinitions




    • ... The Wolfram System follows the principle of trying to put more general definitions after more specific ones. This means that special cases of rules are typically tried before more general cases.

    • Although in many practical cases, the Wolfram System can recognize when one rule is more general than another, you should realize that this is not always possible. For example, if two rules both contain complicated /; conditions, it may not be possible to work out which is more general, and, in fact, there may not be a definite ordering. Whenever the appropriate ordering is not clear, the Wolfram System stores rules in the order you give them.




    ClearAll[g]
    
g[x_?EvenQ] := "even"
    
g[x_?NumberQ] := "number"
    
g /@ {1, 2}



    {"number", "even"}




    ClearAll[h]
    
h[x_?NumberQ] := "number"
    
h[x_?EvenQ] := "even"
    
h /@ {1, 2}



    {"number", "number"}







    share|improve this answer











    $endgroup$


















      6












      $begingroup$

      TheOrderingOfDefinitions




      • ... The Wolfram System follows the principle of trying to put more general definitions after more specific ones. This means that special cases of rules are typically tried before more general cases.

      • Although in many practical cases, the Wolfram System can recognize when one rule is more general than another, you should realize that this is not always possible. For example, if two rules both contain complicated /; conditions, it may not be possible to work out which is more general, and, in fact, there may not be a definite ordering. Whenever the appropriate ordering is not clear, the Wolfram System stores rules in the order you give them.




      ClearAll[g]
      
g[x_?EvenQ] := "even"
      
g[x_?NumberQ] := "number"
      
g /@ {1, 2}



      {"number", "even"}




      ClearAll[h]
      
h[x_?NumberQ] := "number"
      
h[x_?EvenQ] := "even"
      
h /@ {1, 2}



      {"number", "number"}







      share|improve this answer











      $endgroup$
















        6












        6








        6





        $begingroup$

        TheOrderingOfDefinitions




        • ... The Wolfram System follows the principle of trying to put more general definitions after more specific ones. This means that special cases of rules are typically tried before more general cases.

        • Although in many practical cases, the Wolfram System can recognize when one rule is more general than another, you should realize that this is not always possible. For example, if two rules both contain complicated /; conditions, it may not be possible to work out which is more general, and, in fact, there may not be a definite ordering. Whenever the appropriate ordering is not clear, the Wolfram System stores rules in the order you give them.




        ClearAll[g]
        
g[x_?EvenQ] := "even"
        
g[x_?NumberQ] := "number"
        
g /@ {1, 2}



        {"number", "even"}




        ClearAll[h]
        
h[x_?NumberQ] := "number"
        
h[x_?EvenQ] := "even"
        
h /@ {1, 2}



        {"number", "number"}







        share|improve this answer











        $endgroup$



        TheOrderingOfDefinitions




        • ... The Wolfram System follows the principle of trying to put more general definitions after more specific ones. This means that special cases of rules are typically tried before more general cases.

        • Although in many practical cases, the Wolfram System can recognize when one rule is more general than another, you should realize that this is not always possible. For example, if two rules both contain complicated /; conditions, it may not be possible to work out which is more general, and, in fact, there may not be a definite ordering. Whenever the appropriate ordering is not clear, the Wolfram System stores rules in the order you give them.




        ClearAll[g]
        
g[x_?EvenQ] := "even"
        
g[x_?NumberQ] := "number"
        
g /@ {1, 2}



        {"number", "even"}




        ClearAll[h]
        
h[x_?NumberQ] := "number"
        
h[x_?EvenQ] := "even"
        
h /@ {1, 2}



        {"number", "number"}








        share|improve this answer














        share|improve this answer



        share|improve this answer








        edited 2 hours ago

























        answered 2 hours ago









        kglrkglr

        186k10202421




        186k10202421






















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