Trace an empty evaluation chain:

Trace evaluations resulting from local definitions:

Trace the operation of Map:

Trace all expressions used in an evaluation:

Include only those expressions that match _Plus:

Include all evaluations that use transformation rules associated with the symbol Plus:

Obtain evaluations in a trace that match a pattern:

Apply a transformation rule to each match in order to remove the head fib:

Trace the evaluation of conditionals such as If; the 2+2 in the False branch is never evaluated:

Trace the evaluation of logical operations such as And; notice that OddQ[5] is not evaluated:

Trace the evaluation of iteration functions such as Do:

Trace each step in CompoundExpression (;), which has the attribute HoldAll. It evaluates each argument in turn inside the body:

Define a function with no attributes that, like CompoundExpression, returns its last argument:

f[…] evaluates all the arguments prior to entering the body, and then returns the last argument:

Trace the steps in an evaluation where a head with holding attributes is replaced with a head without them:

While the result is the same, the order of evaluation is quite different if there are no holding attributes to begin with:

The function FoldList has no holding attributes:

Internally, it uses nonstandard evaluation to compute the sequence of steps f[x₀,x₁], f[f[x₀,x₁],x₂], …:

By default, symbols such as x match symbols with local names of the form x$nnn:

With MatchLocalNamesFalse, only an explicit match of x will show up:

A recursive definition for finding Fibonacci numbers:

Show only the sums of fib that are encountered:

Show the beginning and the end of the evaluation chain that leads to each sum of fib:

Show the entire evaluation chain that leads to each sum of fib:

Show the evaluation chain leading to the sum, but not what comes after the sum:

A recursive definition for finding Fibonacci numbers:

Show only what additions of positive integers are required:

Show the beginning of the evaluation chain that leads to each addition:

Show all intermediate evaluations that led to each addition:

A recursive definition for finding Fibonacci numbers:

Trace only evaluations through level 3:

fib[6] and fib[7], the starts of the deepest chains, are at level 3 of the result:

A recursive definition for finding Fibonacci numbers:

Show only what evaluations of fib are encountered:

Show only the evaluations of fib and the results:

Show all intermediate evaluations between calls of fib and the result:

Trace evaluation of an expression that evaluates a function g:

Omit evaluations required to get the values of g:

Trace evaluation of an expression that evaluates a function g:

Trace only evaluation inside of g:

Trace evaluation of an expression showing evaluation chains for expressions that change:

Show evaluation chains even for expressions that do not change:

Show the starting point of each evaluation chain, but drop chains that do not change: