Prolog 谓词调用 [英] Prolog predicate calling

问题描述

在以下教程中:http://www.csupomona.edu/~jrfisher/www/prolog_tutorial/7_3.html

有一部分:

test_parser :- repeat,
               write('?? '), 
               read_line(X),
               ( c(F,X,[])   | q(F,X,[])  ),
               nl, write(X), nl, write(F), nl, fail.

现在我对 c(F,X,[]) 和 q(F,X,[]) 部分感到非常困惑，因为它似乎与我见过的任何东西都不匹配，c 只需要一个参数从我可以告诉和这些参数似乎对 q 没有意义.请帮助我了解这里发生了什么.

Now I'm extremely confused about the c(F,X,[]) and q(F,X,[]) part because it doesn't seem to match any thing that I have seen, c only takes one parameter from what I can tell and these parameters don't seem to make sense for q. Please help me understand what is going on here.

推荐答案

c 是用 --> 定义的，它实际上添加了两个隐藏参数.其中第一个是要由语法规则解析的列表；第二个是解析后的剩下的".c(F,X,[]) 调用列表X上的c得到结果F，期望[] 保留，即解析器应该使用整个列表 X.

c is defined with -->, which actually adds two hidden arguments to it. The first of these is a list to be parsed by the grammar rule; the second is "what's left" after the parse. c(F,X,[]) calls c on the list X to obtain a result F, expecting [] to be left, i.e. the parser should consume the entire list X.

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