Parenthesis Selection

The parenthesization of a term slot of a display form is controlled by the parenthesis slot-option of the term slot in the display form definition (the L, E, or * in the 3rd field), by the parens  attribute of the display form filling the term slot, and the relative precedences of the term slot itself and the filling term. The precedence of a term slot is usually that of the display form containing it, although it is possible to assign precedences to individual slots. The parenthesis control works as follows:

• It is only possible to parenthesize the term slot if the filling display form has a parens attribute. If this attribute is absent, the slot is never parenthesized. Therefore the parens attribute must be explicitly added to a display form definition for that definition to ever be parenthesized.

• The parenthesis slot-option controls how precedence affects parenthesization. The parenthesis slot-options have the following meanings:

  L

  Suppress parentheses if display-form precedence is less than child display-form precedence.

  E

  Suppress parentheses if display-form precedence is less than or equal to child display-form precedence.

  *

  Always suppress parentheses.

Note that the L and E options give the behavior you might expect; if they are used in the definitions of infix display forms for the arithmetic terms plus(a;b), and times(a;b), then plus(a;times(b;c)) is displayed as , but times(a;plus(b;c)) is displayed as . With the L and the E options you can set up an infix term as being either right or left associative.

The L, E and * characters in the display of term slot formats are display forms for parenthesization control terms.

  
Table: Slot Options for Parenthesization Control

These terms can be entered using the names shown in Table . The parenthesization control terms also allow the specification of the delimiter characters used for parenthesization, and a precedence for the individual slot. No specific editor support has yet been provided for these features.