This is documentation for Mathematica 8, which was
based on an earlier version of the Wolfram Language.
View current documentation (Version 11.2)
Evaluation Control
Mathematica normally takes any expression it is given, and evaluates it as far as possible. But built into the Mathematica language is a collection of flexible primitives that allow finer control over the process of evaluation in cases where it is needed.
Evaluation Control for Complete Expressions
Hold hold an expression unevaluated
HoldForm display an expression in unevaluated form
Defer display unevaluated, but evaluate if given as Mathematica input
Evaluation Control for Function Arguments
HoldAll, HoldFirst, HoldRest attributes for specifying held function arguments
Evaluate immediately evaluate a function argument
Unevaluated pass a function argument unevaluated
More Detailed Control
ReleaseHold release hold constructs
NHoldAll, NHoldFirst, NHoldRest prevent numerical evaluation of arguments
Manipulating Unevaluated Expressions
With insert variable values without evaluation
Extract extract numbered parts without evaluation
ReplaceAll(/. ▪ ReplacePart  ▪ Delete  ▪ Position
ToString, ToExpression convert to and from string form
Global Evaluation Control
Evaluation in Notebooks
Dynamic  ▪ Refresh  ▪ Evaluator