我正在学习sml并尝试制作一个简化逻辑公式的程序。当我尝试运行此代码时，我总是得到相同的错误，这是我无法弄清楚的。它总是“错误：语法错误：删除BAR ID DARROW”。我附上了以下代码：
- fun Simplify (Or(True, _)) = True
= | Simplify (Or(_, True)) = True
= | Simplify (Or(False, False)) = False
= | Simplify (Or(x, False)) = (Simplify x)
= | Simplify (Or(False, x)) = (Simplify x)
= | Simplify (Or (Var (x), Var (y))) = Or (Var (x), Var (y))
= | Simplify (Or (x, y)) = case Simplify x of
= True => True
= | False => Simplify y
= | x' => case Simplify
= | True => True
GC #0.0.0.0.2.85: (2 ms)
= | False => x'
stdIn:50.6-50.15 Error: syntax error: deleting BAR ID DARROW
- | y' => Or(x', y')
= (*And*)
= | Simplify (And(_, False)) = False
stdIn:2.1-2.8 Error: syntax error: deleting BAR ID DARROW
stdIn:54.1-54.11 Error: syntax error: deleting BAR ID
- | Simplify (And(False, _)) = False
stdIn:1.1-2.6 Error: syntax error: deleting BAR ID
- | Simplify (And(True, True)) = True
= | Simplify (And(True, x)) = (Simplify x)
stdIn:1.1-2.6 Error: syntax error: deleting BAR ID
- | Simplify (And(x, True)) = (Simplify x)
= | Simplify (And(Var (x), Var(y))) = And (Var (x), Var (y))
stdIn:1.1-2.6 Error: syntax error: deleting BAR ID
- | Simplify (And (x, y)) = case Simplify x of
stdIn:1.1-2.6 Error: syntax error: deleting BAR ID
stdIn:53.3-57.4 Error: syntax error: deleting CASE ID
- False => False
= | True => Simplify y
stdIn:2.6-62.6 Error: syntax error: deleting DARROW ID BAR
- | x' => case Simplify y of
= | False => False
stdIn:1.5-2.7 Error: syntax error: deleting BAR ID DARROW
- | True => x'
= | y' => And(x', y')
stdIn:1.5-2.9 Error: syntax error: deleting BAR ID DARROW
- (*Not*)
- | Simplify (Not(Not(x))) = (Simplify x)
= | Simplify (Not(True)) = False
stdIn:68.1-68.11 Error: syntax error: deleting BAR ID
- | Simplify (Not(False)) = True
= | Simplify (Not(Var (x))) = (Not (Var x))
stdIn:1.1-68.3 Error: syntax error: deleting BAR ID
GC #0.0.0.0.3.201: (1 ms)
- | Simplify (Not x) = case Simplify x of
stdIn:1.1-68.3 Error: syntax error: deleting BAR ID
stdIn:68.14-71.4 Error: syntax error: deleting CASE ID
- True => False
= | False => True
stdIn:68.3-74.6 Error: syntax error: deleting DARROW ID BAR
- | x' => Not x'
= (*general*)
= | Simplify True = True
stdIn:1.5-68.4 Error: syntax error: deleting BAR ID DARROW
- | Simplify False = False
= | Simplify (Var(x)) = Var(x);
我添加了整个代码：
datatype formula =
True
| False
| Var of string
| Not of formula
| And of formula * formula
| Or of formula * formula;
fun Simplify (Or(True, _)) = True
| Simplify (Or(_, True)) = True
| Simplify (Or(False, False)) = False
| Simplify (Or(x, False)) = (Simplify x)
| Simplify (Or(False, x)) = (Simplify x)
| Simplify (Or (Var (x), Var (y))) = Or (Var (x), Var (y))
| Simplify (Or (x, y)) = case Simplify x of
True => True
| False => Simplify y
| x' => case Simplify y of
| True => True
| False => x'
| y' => Or(x', y')
(*And*)
| Simplify (And(_, False)) = False
| Simplify (And(False, _)) = False
| Simplify (And(True, True)) = True
| Simplify (And(True, x)) = (Simplify x)
| Simplify (And(x, True)) = (Simplify x)
| Simplify (And(Var (x), Var(y))) = And (Var (x), Var (y))
| Simplify (And (x, y)) = case Simplify x of
False => False
| True => Simplify y
| x' => case Simplify y of
| False => False
| True => x'
| y' => And(x', y')
(*Not*)
| Simplify (Not(Not(x))) = (Simplify x)
| Simplify (Not(True)) = False
| Simplify (Not(False)) = True
| Simplify (Not(Var (x))) = (Not (Var x))
| Simplify (Not x) = case Simplify x of
True => False
| False => True
| x' => Not x'
(*general*)
| Simplify True = True
| Simplify False = False
| Simplify (Var(x)) = Var(x);
答案 0 :(得分：3)
您需要在嵌套的case语句周围使用括号，当使用它们并具有多个函数子句时，因为无法将管道（|）与属于fun子句或case子句区分开来。
在simplify的第二种情况下，你错过了Simplify (Or (x, y))的“y”参数，并且你的一些嵌套的case表达式有一个起始管道，它不应该在：
fun Simplify (Or (True, _)) = True
| Simplify (Or (_, True)) = True
| Simplify (Or (False, False)) = False
| Simplify (Or (x, False)) = Simplify x
| Simplify (Or (False, x)) = Simplify x
| Simplify (Or (Var x, Var y)) = Or (Var x, Var y)
| Simplify (Or (x, y)) = (case Simplify x of
True => True
| False => Simplify y
| x' => (case Simplify y of
True => True
| False => x'
| y' => Or(x', y')))
(*And*)
| Simplify (And (_, False)) = False
| Simplify (And (False, _)) = False
| Simplify (And (True, True)) = True
| Simplify (And (True, x)) = (Simplify x)
| Simplify (And (x, True)) = (Simplify x)
| Simplify (And (Var x, Var y)) = And (Var x, Var y)
| Simplify (And (x, y)) = (case Simplify x of
False => False
| True => Simplify y
| x' => (case Simplify y of
False => False
| True => x'
| y' => And(x', y')))
(*Not*)
| Simplify (Not (Not x)) = (Simplify x)
| Simplify (Not True) = False
| Simplify (Not False) = True
| Simplify (Not (Var x)) = Not (Var x)
| Simplify (Not x) = (case Simplify x of
True => False
| False => True
| x' => Not x')
(*general*)
| Simplify True = True
| Simplify False = False
| Simplify (Var x) = Var x
Atleast用这个相当错误的数据类型编译：
datatype Expr = Or of Expr * Expr
| And of Expr * Expr
| Not of Expr
| Var of Expr
| True
| False