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Mathematica > Core Language > Expressions > Evaluation Control > Hold >

BUILT-IN MATHEMATICA SYMBOL

Hold

Hold[expr]
maintains expr in an unevaluated form.

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:

Out[1]=

Release the hold:

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: