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Hold

✖
Hold[expr]

maintains expr in an unevaluated form.

Details

  • Hold allows you to use an expression that has not undergone normal evaluation.
  • Hold has attribute HoldAll and performs no operation on its arguments.
  • Hold is removed by ReleaseHold. »
  • Hold[e1,e2,…] maintains a sequence of unevaluated expressions to which a function can be applied using Apply.
  • Hold can be inserted as a wrapper by such functions as ToExpression and Extract. »
  • Even though expr itself is not evaluated, Hold[expr] may still evaluate if expr is of the form f[args], and upvalues for f have been defined. »

Examples

open allclose all

Basic Examples  (1)Summary of the most common use cases

Hold an expression to prevent evaluation:

In[1]:=1
✖
https://wolfram.com/xid/0delki-cl7q1t
Out[1]=1

Release the hold:

In[2]:=2
✖
https://wolfram.com/xid/0delki-fgiwf0
Out[2]=2

Scope  (1)Survey of the scope of standard use cases

Extract a part without allowing it to evaluate:

In[1]:=1
✖
https://wolfram.com/xid/0delki-gzoe32
Out[1]=1

Applications  (2)Sample problems that can be solved with this function

Find the length of each expression in a held list without evaluation:

In[1]:=1
✖
https://wolfram.com/xid/0delki-fr3y8d
In[2]:=2
✖
https://wolfram.com/xid/0delki-jcp3r8
Out[2]=2
In[3]:=3
✖
https://wolfram.com/xid/0delki-pnzk20
Out[3]=3

Evaluate every sum (only) inside a held expression:

In[1]:=1
✖
https://wolfram.com/xid/0delki-kpgl84
Out[1]=1
In[2]:=2
✖
https://wolfram.com/xid/0delki-gnnbi2
Out[2]=2
In[3]:=3
✖
https://wolfram.com/xid/0delki-g4jx78
Out[3]=3
In[4]:=4
✖
https://wolfram.com/xid/0delki-ig9mo
Out[4]=4

Properties & Relations  (10)Properties of the function, and connections to other functions

Hold is a container with the attribute HoldAll:

In[1]:=1
✖
https://wolfram.com/xid/0delki-ugxi7
Out[1]=1
In[2]:=2
✖
https://wolfram.com/xid/0delki-iwy1m5
Out[2]=2

Use Evaluate to force evaluation of an argument of Hold:

In[1]:=1
✖
https://wolfram.com/xid/0delki-8fboz
Out[1]=1

Unevaluated inside a held expression is not removed:

In[1]:=1
✖
https://wolfram.com/xid/0delki-bcejf7
Out[1]=1

Sequence splicing still happens inside Hold:

In[1]:=1
✖
https://wolfram.com/xid/0delki-2hgtl
Out[1]=1

Use the container HoldComplete to suppress even such transformations:

In[2]:=2
✖
https://wolfram.com/xid/0delki-byz6s5
Out[2]=2

Upvalues work inside Hold:

In[1]:=1
✖
https://wolfram.com/xid/0delki-bprvkf
In[2]:=2
✖
https://wolfram.com/xid/0delki-mkv4p0
Out[2]=2

They do not work inside HoldComplete:

In[3]:=3
✖
https://wolfram.com/xid/0delki-m1i7w7
In[4]:=4
✖
https://wolfram.com/xid/0delki-lan3jv
Out[4]=4

Substitution works inside Hold:

In[1]:=1
✖
https://wolfram.com/xid/0delki-iu25en
Out[1]=1

Insert into a held expression:

In[1]:=1
✖
https://wolfram.com/xid/0delki-sil
Out[1]=1

ReleaseHold removes one level of Hold:

In[1]:=1
✖
https://wolfram.com/xid/0delki-e2j8iu
Out[1]=1

HoldForm is like Hold but is normally not shown in the output:

In[1]:=1
✖
https://wolfram.com/xid/0delki-of66a
Out[1]=1
In[2]:=2
✖
https://wolfram.com/xid/0delki-l35fd

Hold can be used to freeze the result of ToExpression before it is evaluated:

In[1]:=1
✖
https://wolfram.com/xid/0delki-gwv81u
Out[1]=1
Wolfram Research (1988), Hold, Wolfram Language function, https://reference.wolfram.com/language/ref/Hold.html.
✖
Wolfram Research (1988), Hold, Wolfram Language function, https://reference.wolfram.com/language/ref/Hold.html.

Text

Wolfram Research (1988), Hold, Wolfram Language function, https://reference.wolfram.com/language/ref/Hold.html.

✖
Wolfram Research (1988), Hold, Wolfram Language function, https://reference.wolfram.com/language/ref/Hold.html.

CMS

Wolfram Language. 1988. "Hold." Wolfram Language & System Documentation Center. Wolfram Research. https://reference.wolfram.com/language/ref/Hold.html.

✖
Wolfram Language. 1988. "Hold." Wolfram Language & System Documentation Center. Wolfram Research. https://reference.wolfram.com/language/ref/Hold.html.

APA

Wolfram Language. (1988). Hold. Wolfram Language & System Documentation Center. Retrieved from https://reference.wolfram.com/language/ref/Hold.html

✖
Wolfram Language. (1988). Hold. Wolfram Language & System Documentation Center. Retrieved from https://reference.wolfram.com/language/ref/Hold.html

BibTeX

@misc{reference.wolfram_2025_hold, author="Wolfram Research", title="{Hold}", year="1988", howpublished="\url{https://reference.wolfram.com/language/ref/Hold.html}", note=[Accessed: 23-March-2025 ]}

✖
@misc{reference.wolfram_2025_hold, author="Wolfram Research", title="{Hold}", year="1988", howpublished="\url{https://reference.wolfram.com/language/ref/Hold.html}", note=[Accessed: 23-March-2025 ]}

BibLaTeX

@online{reference.wolfram_2025_hold, organization={Wolfram Research}, title={Hold}, year={1988}, url={https://reference.wolfram.com/language/ref/Hold.html}, note=[Accessed: 23-March-2025 ]}

✖
@online{reference.wolfram_2025_hold, organization={Wolfram Research}, title={Hold}, year={1988}, url={https://reference.wolfram.com/language/ref/Hold.html}, note=[Accessed: 23-March-2025 ]}