内置辅助函数

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有几个新的辅助函数被提出来定位问题和冲突。

替换 _|_：

• error 来启动用户定义消息
• isconcrete 和 exist 来测试或比较

验证器:

• must(expr) passes if expr evaluates to true and fails otherwise
• not(expr) passes if unified with a value x for which expr&x fails and false otherwise.
• numexist(count, ...expr) passes if the number of expressions for which exists(x) evaluates to true unifies with count.
• numconcrete(count, ...expr) passes if the number of expressions for which isconcrete(x) evaluates to true unifies with count.
• numvalid(count, ...expr) passes if the number of expressions for which isvalid(x) evaluates to true unifies with count.

其他:

• manifest(x) evaluates x stripping it of any optional fields and definitions and disambiguating disjunctions after their removal.
• range(from, to, by) creates a stream of values like found in other languages
• head([...]) returns the first element of a list
• Package std would namespace all core builtins under the std package name.

可以通过 core builtin extensions 查看更多细节。