Vjylku

Cat is tipping over bed-side lamps during the night

Saint abbreviation

Why does magnet wire need to be insulated?

What game did these black and yellow dice come from?

A starship is travelling at 0.9c and collides with a small rock. Will it leave a clean hole through, or will more happen?

Short story where statues have their heads replaced by those of carved insect heads

How does one write from a minority culture? A question on cultural references

What is a good reason for every spaceship to carry a weapon on board?

Why did Luke use his left hand to shoot?

Is using an 'empty' metaphor considered bad style?

Airplane generations - how does it work?

Hilchos Shabbos English Sefer

How do I prevent a homebrew Grappling Hook feature from trivializing Tomb of Annihilation?

Why is Agricola named as such?

Has Britain negotiated with any other countries outside the EU in preparation for the exit?

What will happen if Parliament votes "no" on each of the Brexit-related votes to be held on the 12th, 13th and 14th of March?

TikZ graph edges not drawn nicely

What happened to my GE option?

How do you voice extended chords?

What is a DAG (Graph Theory)?

Why does PHOTOREC keep finding files?

Why is it that Bernie Sanders is always called a "socialist"?

In Linux what happens if 1000 files in a directory are moved to another location while another 300 files were added to the source directory?

After checking in online, how do I know whether I need to go show my passport at airport check-in?

Is there a defined priority for pattern matching?

Using a PatternTest versus a Condition for pattern matchingIs pure pattern matching without PatternTest and Condition Turing-complete?Classifying poker hands by pattern matchingMore general pattern fails to match everything the more specific pattern does.Detecting a more general patternPattern matching to head with HoldFirstHow to visualize pattern matching process?Pattern matching an expression involving TimesCompare arrays using custom pattern matchingPattern Match Bug with Equals?

3

$begingroup$

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

edited 1 hour ago

wgoodall01

asked 1 hour ago

wgoodall01wgoodall01

1185

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♦
  1 hour ago
  
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  That's right---fixed.
  $endgroup$
  – wgoodall01
  1 hour 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♦
  1 hour ago
  
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

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

  
  
  
  

add a comment | 

3

$begingroup$

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

edited 1 hour ago

wgoodall01

asked 1 hour ago

wgoodall01wgoodall01

1185

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♦
  1 hour ago
  
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  That's right---fixed.
  $endgroup$
  – wgoodall01
  1 hour 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♦
  1 hour ago
  
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

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

  
  
  
  

add a comment | 

$begingroup$

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

edited 1 hour ago

wgoodall01

asked 1 hour ago

wgoodall01wgoodall01

1185

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.

$endgroup$

g[x_?EvenQ] := "even"    

g[x_?NumberQ] := "number"

share|improve this question

edited 1 hour ago

wgoodall01

asked 1 hour ago

wgoodall01wgoodall01

1185

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

edited 1 hour ago

wgoodall01

asked 1 hour ago

wgoodall01wgoodall01

1185

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 1 hour ago

wgoodall01wgoodall01

1185

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 1 hour ago

wgoodall01wgoodall01

1185

1 Answer
1

active

oldest

votes

4

$begingroup$

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

edited 1 hour ago

answered 1 hour ago

kglrkglr

186k10202421

$endgroup$

add a comment | 

Your Answer

StackExchange.ifUsing("editor", function () {
return StackExchange.using("mathjaxEditing", function () {
StackExchange.MarkdownEditor.creationCallbacks.add(function (editor, postfix) {
StackExchange.mathjaxEditing.prepareWmdForMathJax(editor, postfix, [["$", "$"], ["\\(","\\)"]]);
});
});
}, "mathjax-editing");

StackExchange.ready(function() {
var channelOptions = {
tags: "".split(" "),
id: "387"
};
initTagRenderer("".split(" "), "".split(" "), channelOptions);

StackExchange.using("externalEditor", function() {
// Have to fire editor after snippets, if snippets enabled
if (StackExchange.settings.snippets.snippetsEnabled) {
StackExchange.using("snippets", function() {
createEditor();
});
}
else {
createEditor();
}
});

function createEditor() {
StackExchange.prepareEditor({
heartbeatType: 'answer',
autoActivateHeartbeat: false,
convertImagesToLinks: false,
noModals: true,
showLowRepImageUploadWarning: true,
reputationToPostImages: null,
bindNavPrevention: true,
postfix: "",
imageUploader: {
brandingHtml: "Powered by u003ca class="icon-imgur-white" href="https://imgur.com/"u003eu003c/au003e",
contentPolicyHtml: "User contributions licensed under u003ca href="https://creativecommons.org/licenses/by-sa/3.0/"u003ecc by-sa 3.0 with attribution requiredu003c/au003e u003ca href="https://stackoverflow.com/legal/content-policy"u003e(content policy)u003c/au003e",
allowUrls: true
},
onDemand: true,
discardSelector: ".discard-answer"
,immediatelyShowMarkdownHelp:true
});


}
});

wgoodall01 is a new contributor. Be nice, and check out our Code of Conduct.

draft saved

draft discarded

Sign up or log in

StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});

Sign up using Google

Sign up using Facebook

Sign up using Email and Password

Post as a guest

Name

Email

Required, but never shown

StackExchange.ready(
function () {
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fmathematica.stackexchange.com%2fquestions%2f192278%2fis-there-a-defined-priority-for-pattern-matching%23new-answer', 'question_page');
}
);

Post as a guest

Name

Email

Required, but never shown

4

$begingroup$

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

edited 1 hour ago

answered 1 hour ago

kglrkglr

186k10202421

$endgroup$

add a comment | 

4

$begingroup$

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

edited 1 hour ago

answered 1 hour ago

kglrkglr

186k10202421

$endgroup$

add a comment | 

$begingroup$

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

edited 1 hour ago

answered 1 hour ago

kglrkglr

186k10202421

$endgroup$

ClearAll[g]

g[x_?EvenQ] := "even"

g[x_?NumberQ] := "number"

g /@ {1, 2}

ClearAll[h]

h[x_?NumberQ] := "number"

h[x_?EvenQ] := "even"

h /@ {1, 2}

share|improve this answer

edited 1 hour ago

answered 1 hour ago

kglrkglr

186k10202421

answered 1 hour ago

kglrkglr

186k10202421

answered 1 hour ago

kglrkglr

186k10202421