Environment variables can be used in a simple assignment.  In a procedure body, the assignment is automatically undone on exit from the procedure.  The value of the environment variable is available to all subprocedures called from that procedure, unless locally superseded.

The following is a list of predefined environment variables:

A variable with name beginning with "_Env" is considered an environment variable.

 , , and  are the results of the last, second last, and third last computation in the current environment.

Digits is the number of significant digits used for floating-point operations, and is set to 10 initially.

mod is set to `modp` initially.

Normalizer is set to `normal` initially, and is used by the kernel in series to normalize leading terms of divisors.

Order represents the order of series calculations performed by Maple. It does not represent the order of the series output. Order is set to 6 initially.

The setting of printlevel causes the display of the results of all statements executed up to the level indicated by printlevel. Initially, printlevel is set to 1.

Testzero is initialized with proc() evalb(Normalizer(args[1]) = 0) end proc, which is a relatively trivial test for zero.  Testzero is used in the kernel by series, when it needs to determine whether a leading coefficient is zero for division. In principle, every test for zero and every call to normal should be done using these functions.

The call anames('environment') returns a sequence of all the currently active environment variables. Note that an _Env variable is not considered to be an environment variable at the top level; only once execution is inside a procedure is an environment set up to protect the top-level value of the variable. So, _Env variables only show up if these variables are modified within a procedure, and anames('environment') is called from within the procedure or at a deeper level of execution.

t := proc() Digits := Digits + 4;  end proc:

p := proc() _Envy := bar end proc:

p := proc() _Envy := bar; anames(environment) end proc: