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Hold

Hold[expr]
maintains expr in an unevaluated form.
  • Hold has attribute HoldAll, and performs no operation on its arguments.
  • Hold maintains a sequence of unevaluated expressions to which a function can be applied using Apply.
  • Even though expr itself is not evaluated, Hold[expr] may still evaluate if expr is of the form , and upvalues for f have been defined. »
Hold an expression to prevent evaluation:
Release the hold:
Hold an expression to prevent evaluation:
In[1]:=
Click for copyable input
Out[1]=
Release the hold:
In[2]:=
Click for copyable input
Out[2]=
Find the length of each expression in a held list without evaluation:
Evaluate every sum (only) inside a held expression:
Hold is a container with the attribute HoldAll:
Use Evaluate to force evaluation of an argument of Hold:
Unevaluated inside a held expression is not removed:
Sequence splicing still happens inside Hold:
Use the container HoldComplete to suppress even such transformations:
Upvalues work inside Hold:
They do not work inside HoldComplete:
Substitution works inside Hold:
Insert into a held expression:
ReleaseHold removes one level of Hold:
HoldForm is like Hold, but is normally not shown in the output:
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