Unevaluated Expressions, 'expr' - Maple Programming Help

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Unevaluated Expressions, 'expr'

 

Description

Examples

Description

• 

Enclosing an expression with right single quotes ' ' will delay the evaluation of the expression.

• 

As another example, help(Digits); returns a message stating that the argument to the help function was not a name --- because Digits evaluates to an integer value. To get the desired help description, use instead the quoted form: help('Digits');.

• 

Enclosing an expression in unevaluation quotes produces a new expression of type uneval. It evaluates to the original expression.

• 

After each evaluation, one level of single quotes is stripped off.

• 

Note that evaluation is different from simplification.

• 

A special case of unevaluation is used to unassign a name. In some cases, the evaln function is required to unassign a name, such as: foritondoai:=evalnaienddo; where i must be evaluated but ai must not be fully evaluated.

• 

It is important to quote name arguments passed to procedures, such as type names, or options to other procedures.

• 

There is also a procedure parameter modifier, uneval, which declares that an argument to a procedure is automatically left unevaluated.

Examples

x2:

y3:

f'x+y'

f:=x+y

(1)

5

(2)

After each evaluation, one level of single quotes is stripped off.

a1

a:=1

(3)

''a''

'a'

(4)

'a'

a

(5)

a

1

(6)

'2'

2

(7)

Name arguments passed to procedures must be in quotes.

dependent2:

types,'dependents,t'

true

(8)

types,dependents,t

false

(9)

A special case of unevaluation is used to unassign a name.

x5

x:=5

(10)

x'x'

x:=x

(11)

x

x

(12)

See Also

assignment

evaln

spec_eval_rules

The uneval Modifier

type[uneval]

 


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