Is there a defined priority for pattern matching?
$begingroup$
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
New contributor
$endgroup$
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
New contributor
$endgroup$
$begingroup$
g[x_NumberQ]
means to match arguments with the headNumberQ
. What you want is to match arguments such thatNumberQ[x]
isTrue
, which isg[x_?NumberQ]
. Look upPatternTest
. (Before you make this correction, make sure to runClear[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, evaluateDownValues[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
50 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
New contributor
$endgroup$
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
New contributor
New contributor
edited 2 hours ago
wgoodall01
New contributor
asked 2 hours ago
wgoodall01wgoodall01
1185
1185
New contributor
New contributor
$begingroup$
g[x_NumberQ]
means to match arguments with the headNumberQ
. What you want is to match arguments such thatNumberQ[x]
isTrue
, which isg[x_?NumberQ]
. Look upPatternTest
. (Before you make this correction, make sure to runClear[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, evaluateDownValues[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
50 mins ago
add a comment |
$begingroup$
g[x_NumberQ]
means to match arguments with the headNumberQ
. What you want is to match arguments such thatNumberQ[x]
isTrue
, which isg[x_?NumberQ]
. Look upPatternTest
. (Before you make this correction, make sure to runClear[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, evaluateDownValues[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
50 mins 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
50 mins ago
$begingroup$
Or just execute
?g
to see the order of the definitions.$endgroup$
– Roman
50 mins ago
add a comment |
1 Answer
1
active
oldest
votes
$begingroup$
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"}
$endgroup$
add a comment |
Your Answer
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1 Answer
1
active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
$begingroup$
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"}
$endgroup$
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"}
$endgroup$
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"}
$endgroup$
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"}
edited 1 hour ago
answered 2 hours ago
kglrkglr
186k10202421
186k10202421
add a comment |
add a comment |
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$begingroup$
g[x_NumberQ]
means to match arguments with the headNumberQ
. What you want is to match arguments such thatNumberQ[x]
isTrue
, which isg[x_?NumberQ]
. Look upPatternTest
. (Before you make this correction, make sure to runClear[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
50 mins ago