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based on an earlier version of the Wolfram Language.
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TagSet


assigns rhs to be the value of lhs, and associates the assignment with the symbol f.
  • TagSet defines upvalues or downvalues as appropriate.
  • The symbol f in must appear in lhs as the head of lhs, the head of the head, one of the elements of lhs, or the head of one of the elements.
  • A common case is .
  • You can see all the rules associated with a particular symbol by typing ?symbol.
  • If f appears several times in lhs, then associates the assignment with each occurrence.
  • When it appears in unevaluated symbolic form, TagSet is treated as a scoping construct so that variables in nested occurrences are renamed if necessary.
Define a symbolic property of a symbol:
Define a symbolic property of a symbol:
In[1]:=
Click for copyable input
Out[1]=
For ownvalues, the tag is redundant:
For downvalues, the tag is redundant:
Use a tag to define upvalues:
Build a database of exchange rates:
defines upvalues in the same way as using a tag does:
The right side of an immediate definition is evaluated when the definition is made:
The right side of a delayed definition is evaluated each time the definition is used:
Definitions with the same left side overwrite earlier ones:
Definition prints definitions associated with a symbol:
Information prints various information about a symbol, including any definitions:
UpValues returns a list of rules corresponding to any upvalues defined:
Use to clear definitions with a particular left-hand side:
Clear all definitions:
In the presence of global variables, pattern variables may show unexpected behavior:
Delayed assignments behave as expected:
Use upvalues to assign to subscripted variables:
Subscripted variables are distinct from indexed variables:
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