忽略 Isabelle 中缺失的模式
Ignore missing pattern in Isabelle
例如，我想定义一个提取列表第一个元素的函数。对于这个函数，我不关心列表为空的情况（例如，我可以确保每次使用该函数时，我都会传递一个非空列表）。但伊莎贝尔会警告说
Missing patterns in function definition:
extracts [] = undefined
我该如何处理这种情况？
您有很多选择，例如：
fun extracts where "extracts xs = hd xs"definition extracts where [simp]: "extracts = hd"fun extracts where "extracts xs = (case xs of (x # _) ⇒ x)"fun extracts where "extracts (x # _) = x" | "extracts [] = undefined"
例如，我想定义一个提取列表第一个元素的函数。对于这个函数，我不关心列表为空的情况（例如，我可以确保每次使用该函数时，我都会传递一个非空列表）。但伊莎贝尔会警告说
Missing patterns in function definition:
extracts [] = undefined
我该如何处理这种情况？
您有很多选择，例如：
fun extracts where "extracts xs = hd xs"definition extracts where [simp]: "extracts = hd"fun extracts where "extracts xs = (case xs of (x # _) ⇒ x)"fun extracts where "extracts (x # _) = x" | "extracts [] = undefined"