Controlling parenthesis while working with operators

懵懂的女人 提交于 2021-02-11 15:18:30

问题


When working with user-defined operators, Prolog sometimes adds / removes parenthesis to expressions involving those operators automatically. Is there a way to control this?

Many thanks


回答1:


The parens are just added by portray. They're not part of the internal representation of the code. You can override portray to change how things are printed. see portray_text




回答2:


An operator is defined like so:

:- op(Precedence, Associativity, Operator).

This answer to a similar question explains this, but the short answer is that the Associativity option controls this; xfy makes an operator left-associative and yfx makes an operator right associative. The Precedence tells Prolog how to decide which operator is the subexpression when it sees more than one.



来源:https://stackoverflow.com/questions/15175400/controlling-parenthesis-while-working-with-operators

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