Expressions
At the core of the Wolfram Language is the foundational idea that everything—data, programs, formulas, graphics, documents—can be represented as symbolic expressions. And it is this unifying concept that underlies the Wolfram Language's symbolic programming paradigm, and makes possible much of the unique power of the Wolfram Language and the Wolfram System.
Expression Structure »
FullForm — the full form of an expression, without shortened syntax
TreeForm ▪ Head ▪ Length ▪ Depth ▪ Symbol ▪ Construct ▪ ...
Common General-Purpose Expression Types
List ▪ Association ▪ Dataset ▪ Rule
Transforming Expressions »
expr/.rules — make replacements for any occurrence of a pattern in an expression
Applying Functions »
Map, Apply — map, apply a function at any level in any expression
Expression Testing »
SameQ (===) ▪ FreeQ ▪ MemberQ ▪ NumberQ ▪ OrderedQ ▪ ...
Parts of Expressions »
Part (..[[..]]) — numbered parts of an expression, reset using =
Position ▪ ReplacePart ▪ MapAt ▪ ReplaceAt ▪ Delete ▪ ...
Cases — find occurrences of a pattern in an expression
Structural Operations »
Flatten ▪ Thread ▪ Distribute ▪ FlattenAt ▪ Append ▪ ...
Controlling Expression Evaluation »
Hold ▪ Evaluate ▪ HoldFirst ▪ HoldAll ▪ Inactive ▪ ...