How can you Unset the following UpValues?

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8
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This expression is taken from a talk given by the late Robby Villegas. The UpValues to some symbol a is defined below as:

ClearAll["a"];
a /: _[___, a, ___] := (Print["a fired"]; Null)

Nothing I tried could Clear the definitions associated with the symbol. Is there a way to clear the associated UpValues.

edited Sep 8 at 17:44

Carl Woll

56.3k272147

asked Sep 8 at 14:22

Ali Hashmi

5,49931330

4

Regardless of the method to solve this problem, I will mention that giving such generic UpValues to symbols is outright dangerous. Speaking from experience here, I have tried to use this kind of rules before, and it was invariably biting me later - so I never ended up leaving such constructs in final code in whatever I was doing.
â€“Â Leonid Shifrin
Sep 8 at 17:33

add a commentÂ |Â

up vote
8
down vote

favorite

This expression is taken from a talk given by the late Robby Villegas. The UpValues to some symbol a is defined below as:

ClearAll["a"];
a /: _[___, a, ___] := (Print["a fired"]; Null)

Nothing I tried could Clear the definitions associated with the symbol. Is there a way to clear the associated UpValues.

edited Sep 8 at 17:44

Carl Woll

56.3k272147

asked Sep 8 at 14:22

Ali Hashmi

5,49931330

4

Regardless of the method to solve this problem, I will mention that giving such generic UpValues to symbols is outright dangerous. Speaking from experience here, I have tried to use this kind of rules before, and it was invariably biting me later - so I never ended up leaving such constructs in final code in whatever I was doing.
â€“Â Leonid Shifrin
Sep 8 at 17:33

add a commentÂ |Â

up vote
8
down vote

favorite

This expression is taken from a talk given by the late Robby Villegas. The UpValues to some symbol a is defined below as:

ClearAll["a"];
a /: _[___, a, ___] := (Print["a fired"]; Null)

Nothing I tried could Clear the definitions associated with the symbol. Is there a way to clear the associated UpValues.

edited Sep 8 at 17:44

Carl Woll

56.3k272147

asked Sep 8 at 14:22

Ali Hashmi

5,49931330

This expression is taken from a talk given by the late Robby Villegas. The UpValues to some symbol a is defined below as:

ClearAll["a"];
a /: _[___, a, ___] := (Print["a fired"]; Null)

Nothing I tried could Clear the definitions associated with the symbol. Is there a way to clear the associated UpValues.

edited Sep 8 at 17:44

Carl Woll

56.3k272147

asked Sep 8 at 14:22

Ali Hashmi

5,49931330

edited Sep 8 at 17:44

Carl Woll

56.3k272147

edited Sep 8 at 17:44

Carl Woll

56.3k272147

edited Sep 8 at 17:44

Carl Woll

56.3k272147

asked Sep 8 at 14:22

Ali Hashmi

5,49931330

asked Sep 8 at 14:22

Ali Hashmi

5,49931330

asked Sep 8 at 14:22

Ali Hashmi

5,49931330

4

Regardless of the method to solve this problem, I will mention that giving such generic UpValues to symbols is outright dangerous. Speaking from experience here, I have tried to use this kind of rules before, and it was invariably biting me later - so I never ended up leaving such constructs in final code in whatever I was doing.
â€“Â Leonid Shifrin
Sep 8 at 17:33

add a commentÂ |Â

4

Regardless of the method to solve this problem, I will mention that giving such generic UpValues to symbols is outright dangerous. Speaking from experience here, I have tried to use this kind of rules before, and it was invariably biting me later - so I never ended up leaving such constructs in final code in whatever I was doing.
â€“Â Leonid Shifrin
Sep 8 at 17:33

Regardless of the method to solve this problem, I will mention that giving such generic UpValues to symbols is outright dangerous. Speaking from experience here, I have tried to use this kind of rules before, and it was invariably biting me later - so I never ended up leaving such constructs in final code in whatever I was doing.
â€“Â Leonid Shifrin
Sep 8 at 17:33

add a commentÂ |Â

2 Answers
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up vote
9
down vote

Note that you could clear all of the *Values by using Clear["a"] or ClearAll["a"]. However, if you only want to clear this particular UpValues you could make use of the fact that HoldAllComplete prevents UpValues from firing. So, temporarily give TagUnset this attribute. Here's your UpValues definition:

ClearAll["a"];
a /: _[___,a,___] := (Print["a fired"];Null)

Give TagUnset the HoldAllComplete attribute, and unset the above definition:

Internal`InheritedBlock[TagUnset,
 SetAttributes[TagUnset, HoldAllComplete];
 TagUnset[a, _[___,a,___]]
]

Check:

UpValues[a]

edited Sep 8 at 17:20

answered Sep 8 at 16:50

Carl Woll

56.3k272147

Thanks. Very neat.
â€“Â Ali Hashmi
2 days ago

add a commentÂ |Â

up vote
6
down vote

a /: Except[TagUnset, _][___, a, ___] := (Print["a fired"]; Null);

f[a]
(* a fired *)

(* As we can see below, usage of ClearAll does not work *)

ClearAll[a]
(* a fired *)


(* now removing the associated values using the TagUnset Head *)

TagUnset[Unevaluated[a],HoldPattern[Except[TagUnset, _][___, a, ___]]];

f[a]
(* f[a] *)

answered Sep 8 at 14:22

Ali Hashmi

5,49931330

I think both the Unevaluated and the HoldPattern are unnecessary.
â€“Â Carl Woll
Sep 9 at 6:48

@Carl .. though unnecessary but I think it is a safe practice
â€“Â Ali Hashmi
2 days ago

add a commentÂ |Â

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2 Answers
2

active

oldest

votes

2 Answers
2

active

oldest

votes

up vote
9
down vote

ClearAll["a"];
a /: _[___,a,___] := (Print["a fired"];Null)

Give TagUnset the HoldAllComplete attribute, and unset the above definition:

Internal`InheritedBlock[TagUnset,
 SetAttributes[TagUnset, HoldAllComplete];
 TagUnset[a, _[___,a,___]]
]

Check:

UpValues[a]

edited Sep 8 at 17:20

answered Sep 8 at 16:50

Carl Woll

56.3k272147

Thanks. Very neat.
â€“Â Ali Hashmi
2 days ago

add a commentÂ |Â

up vote
9
down vote

ClearAll["a"];
a /: _[___,a,___] := (Print["a fired"];Null)

Give TagUnset the HoldAllComplete attribute, and unset the above definition:

Internal`InheritedBlock[TagUnset,
 SetAttributes[TagUnset, HoldAllComplete];
 TagUnset[a, _[___,a,___]]
]

Check:

UpValues[a]

edited Sep 8 at 17:20

answered Sep 8 at 16:50

Carl Woll

56.3k272147

Thanks. Very neat.
â€“Â Ali Hashmi
2 days ago

add a commentÂ |Â

up vote
9
down vote

ClearAll["a"];
a /: _[___,a,___] := (Print["a fired"];Null)

Give TagUnset the HoldAllComplete attribute, and unset the above definition:

Internal`InheritedBlock[TagUnset,
 SetAttributes[TagUnset, HoldAllComplete];
 TagUnset[a, _[___,a,___]]
]

Check:

UpValues[a]

edited Sep 8 at 17:20

answered Sep 8 at 16:50

Carl Woll

56.3k272147

ClearAll["a"];
a /: _[___,a,___] := (Print["a fired"];Null)

Give TagUnset the HoldAllComplete attribute, and unset the above definition:

Internal`InheritedBlock[TagUnset,
 SetAttributes[TagUnset, HoldAllComplete];
 TagUnset[a, _[___,a,___]]
]

Check:

UpValues[a]

edited Sep 8 at 17:20

answered Sep 8 at 16:50

Carl Woll

56.3k272147

edited Sep 8 at 17:20

answered Sep 8 at 16:50

Carl Woll

56.3k272147

answered Sep 8 at 16:50

Carl Woll

56.3k272147

answered Sep 8 at 16:50

Carl Woll

56.3k272147

Thanks. Very neat.
â€“Â Ali Hashmi
2 days ago

add a commentÂ |Â

Thanks. Very neat.
â€“Â Ali Hashmi
2 days ago

Thanks. Very neat.
â€“Â Ali Hashmi
2 days ago

add a commentÂ |Â

up vote
6
down vote

a /: Except[TagUnset, _][___, a, ___] := (Print["a fired"]; Null);

f[a]
(* a fired *)

(* As we can see below, usage of ClearAll does not work *)

ClearAll[a]
(* a fired *)


(* now removing the associated values using the TagUnset Head *)

TagUnset[Unevaluated[a],HoldPattern[Except[TagUnset, _][___, a, ___]]];

f[a]
(* f[a] *)

answered Sep 8 at 14:22

Ali Hashmi

5,49931330

I think both the Unevaluated and the HoldPattern are unnecessary.
â€“Â Carl Woll
Sep 9 at 6:48

@Carl .. though unnecessary but I think it is a safe practice
â€“Â Ali Hashmi
2 days ago

add a commentÂ |Â

up vote
6
down vote

a /: Except[TagUnset, _][___, a, ___] := (Print["a fired"]; Null);

f[a]
(* a fired *)

(* As we can see below, usage of ClearAll does not work *)

ClearAll[a]
(* a fired *)


(* now removing the associated values using the TagUnset Head *)

TagUnset[Unevaluated[a],HoldPattern[Except[TagUnset, _][___, a, ___]]];

f[a]
(* f[a] *)

answered Sep 8 at 14:22

Ali Hashmi

5,49931330

I think both the Unevaluated and the HoldPattern are unnecessary.
â€“Â Carl Woll
Sep 9 at 6:48

@Carl .. though unnecessary but I think it is a safe practice
â€“Â Ali Hashmi
2 days ago

add a commentÂ |Â

up vote
6
down vote

a /: Except[TagUnset, _][___, a, ___] := (Print["a fired"]; Null);

f[a]
(* a fired *)

(* As we can see below, usage of ClearAll does not work *)

ClearAll[a]
(* a fired *)


(* now removing the associated values using the TagUnset Head *)

TagUnset[Unevaluated[a],HoldPattern[Except[TagUnset, _][___, a, ___]]];

f[a]
(* f[a] *)

answered Sep 8 at 14:22

Ali Hashmi

5,49931330

a /: Except[TagUnset, _][___, a, ___] := (Print["a fired"]; Null);

f[a]
(* a fired *)

(* As we can see below, usage of ClearAll does not work *)

ClearAll[a]
(* a fired *)


(* now removing the associated values using the TagUnset Head *)

TagUnset[Unevaluated[a],HoldPattern[Except[TagUnset, _][___, a, ___]]];

f[a]
(* f[a] *)

answered Sep 8 at 14:22

Ali Hashmi

5,49931330

answered Sep 8 at 14:22

Ali Hashmi

5,49931330

answered Sep 8 at 14:22

Ali Hashmi

5,49931330

answered Sep 8 at 14:22

Ali Hashmi

5,49931330

I think both the Unevaluated and the HoldPattern are unnecessary.
â€“Â Carl Woll
Sep 9 at 6:48

@Carl .. though unnecessary but I think it is a safe practice
â€“Â Ali Hashmi
2 days ago

add a commentÂ |Â

I think both the Unevaluated and the HoldPattern are unnecessary.
â€“Â Carl Woll
Sep 9 at 6:48

@Carl .. though unnecessary but I think it is a safe practice
â€“Â Ali Hashmi
2 days ago

I think both the Unevaluated and the HoldPattern are unnecessary.
â€“Â Carl Woll
Sep 9 at 6:48

@Carl .. though unnecessary but I think it is a safe practice
â€“Â Ali Hashmi
2 days ago

add a commentÂ |Â

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