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Mathematica > Core Language > Expressions > Evaluation Control > HoldFirst >

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HoldFirst

HoldFirst
is an attribute which specifies that the first argument to a function is to be maintained in an unevaluated form.

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Definitions for unevaluated expressions can implement call-by-name semantics:

The global variable has been modified:

Functions that operate on symbols often need the HoldFirst attribute:

Assignments do not evaluate their left-hand sides:

Use Evaluate to force evaluation of an argument of a HoldFirst function:

Suppress the evaluation of the first argument of a pure function:

Sequence splitting still happens for HoldFirst functions:

NHoldFirst protects arguments from N, but evaluates them normally otherwise:

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