Unevaluated Expressions, 'expr'
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: for⁢i⁢to⁢n⁢do⁢⁢ai:=evaln⁡ai⁢end⁢do; 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.
x ≔ 2:
y ≔ 3:
f ≔ 'x+y'
f ≔ x+y
a ≔ 1
Name arguments passed to procedures must be in quotes.
dependent ≔ 2:
A special case of unevaluation is used to unassign a name.
x ≔ 5
x ≔ 'x'
x ≔ x
The uneval Modifier
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