Give the function f the attribute HoldAll:

As a result, the first argument is not evaluated prior to entering the (in this case nonexistent) function body:

Compare with a function g that has no attributes:

SetAttributes does not evaluate the symbols in its first argument:

As a result, the preceding input set the attribute on f, not c:

This is made possible by the fact that SetAttributes has the attribute HoldFirst:

Give the function inout the attribute HoldFirst:

Define a function of two arguments that returns them wrapped in Hold as well as the first without wrapping:

The second argument is evaluated prior to entering the function body, while the first is evaluated inside the function body:

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: