以下类型显然非常大，因此手动编写代码将其转换为可读形式会很乏味。我想知道以可读形式显示树的最简单方法。
type Element =
| Nil
| Token of Token
| Expression of Element * Element
| ExpressionNoIn of Element * Element
| AssignmentExpression of Element * AssignmentOperator * Element
| AssignmentExpressionNoIn of Element * AssignmentOperator * Element
| ConditionalExpression of Element * Element * Element
| ConditionalExpressionNoIn of Element * Element * Element
| LogicalORExpression of Element * Element
| LogicalORExpressionNoIn of Element * Element
| LogicalANDExpression of Element * Element
| LogicalANDExpressionNoIn of Element * Element
| BitwiseORExpression of Element * Element
| BitwiseORExpressionNoIn of Element * Element
| BitwiseXORExpression of Element * Element
| BitwiseXORExpressionNoIn of Element * Element
| BitwiseANDExpression of Element * Element
| BitwiseANDExpressionNoIn of Element * Element
| EqualityExpression of Element * EqualityOperator * Element
| EqualityExpressionNoIn of Element * EqualityOperator * Element
| RelationalExpression of Element * RelationalOperator * Element
| RelationalExpressionNoIn of Element * RelationalOperator * Element
| ShiftExpression of Element * BitwiseShiftOperator * Element
| AdditiveExpression of Element * AdditiveOperator * Element
| MultiplicativeExpression of Element * MultiplicativeOperator * Element
| UnaryExpression of UnaryOperator * Element
| PostfixExpression of Element * PostfixOperator
| MemberExpression of Element * Element
| Arguments of Element * Element
| ArgumentList of Element
| CallExpression of Element * Element
| NewExpression of NewOperator * Element
| LeftHandSideExpression of Element
| PrimaryExpression of Element
| ObjectLiteral of Element
| PropertyNameAndValueList of Element * Element
| PropertyAssignment of Element * Element * Element
| PropertyName of Element
| PropertySetParameterList of Element
| ArrayLiteral of Element * Element
| Elision of Element * Element
| ElementList of Element * Element * Element
| Statement of Element
| Block of Element
| StatementList of Element * Element
| VariableStatement of Element
| VariableDeclarationList of Element * Element
| VariableDeclarationListNoIn of Element * Element
| VariableDeclaration of Element * Element
| VariableDeclarationNoIn of Element * Element
| Initialiser of Element
| InitialiserNoIn of Element
| EmptyStatement
| ExpressionStatement of Element
| IfStatement of Element * Element * Element
| IterationStatement of Element * Element * Element * Element
| ContinueStatement of Element
| BreakStatement of Element
| ReturnStatement of Element
| WithStatement of Element * Element
| SwitchStatement of Element * Element
| CaseBlock of Element * Element * Element
| CaseClauses of Element * Element
| CaseClause of Element * Element
| DefaultClause of Element
| LabelledStatement of Element * Element
| ThrowStatement of Element
| TryStatement of Element * Element * Element
| Catch of Element * Element
| Finally of Element
| DebuggerStatement
| FunctionDeclaration of Element * Element * Element
| FunctionExpression of Element * Element * Element
| FormalParameterList of Element * Element
| FunctionBody of Element
| SourceElement of Element
| SourceElements of Element * Element
| Program of Element
下面是一个如何显示的示例。 (和我前段时间制作的有点不同。)
<Expression>
<AssignmentExpression>
<ConditionalExpression>
<LogicalORExpression>
<LogicalORExpression>
<LogicalANDExpression>
<BitwiseORExpression>
<BitwiseXORExpression>
<BitwiseANDExpression>
<EqualityExpression>
<EqualityExpression>
<RelationalExpression>
<ShiftExpression>
<AdditiveExpression>
<MultiplicativeExpression>
<MultiplicativeExpression>
<UnaryExpression>
<PostfixExpression>
<LeftHandSideExpression>
<NewExpression>
<MemberExpression>
<PrimaryExpression>
<TokenNode Value="i" Line="9" Column="13" />
</PrimaryExpression>
</MemberExpression>
</NewExpression>
</LeftHandSideExpression>
</PostfixExpression>
</UnaryExpression>
</MultiplicativeExpression>
<TokenNode Value="%" Line="9" Column="15" />
<UnaryExpression>
<PostfixExpression>
<LeftHandSideExpression>
<NewExpression>
<MemberExpression>
<PrimaryExpression>
<TokenNode Value="3" Line="9" Column="17" />
</PrimaryExpression>
</MemberExpression>
</NewExpression>
</LeftHandSideExpression>
</PostfixExpression>
</UnaryExpression>
</MultiplicativeExpression>
</AdditiveExpression>
</ShiftExpression>
</RelationalExpression>
</EqualityExpression>
<TokenNode Value="===" Line="9" Column="19" />
<RelationalExpression>
<ShiftExpression>
<AdditiveExpression>
<MultiplicativeExpression>
<UnaryExpression>
<PostfixExpression>
<LeftHandSideExpression>
<NewExpression>
<MemberExpression>
<PrimaryExpression>
<TokenNode Value="0" Line="9" Column="23" />
</PrimaryExpression>
</MemberExpression>
</NewExpression>
</LeftHandSideExpression>
</PostfixExpression>
</UnaryExpression>
</MultiplicativeExpression>
</AdditiveExpression>
</ShiftExpression>
</RelationalExpression>
</EqualityExpression>
</BitwiseANDExpression>
</BitwiseXORExpression>
</BitwiseORExpression>
</LogicalANDExpression>
</LogicalORExpression>
<TokenNode Value="||" Line="9" Column="25" />
<LogicalANDExpression>
<BitwiseORExpression>
<BitwiseXORExpression>
<BitwiseANDExpression>
<EqualityExpression>
<EqualityExpression>
<RelationalExpression>
<ShiftExpression>
<AdditiveExpression>
<MultiplicativeExpression>
<MultiplicativeExpression>
<UnaryExpression>
<PostfixExpression>
<LeftHandSideExpression>
<NewExpression>
<MemberExpression>
<PrimaryExpression>
<TokenNode Value="i" Line="9" Column="28" />
</PrimaryExpression>
</MemberExpression>
</NewExpression>
</LeftHandSideExpression>
</PostfixExpression>
</UnaryExpression>
</MultiplicativeExpression>
<TokenNode Value="%" Line="9" Column="30" />
<UnaryExpression>
<PostfixExpression>
<LeftHandSideExpression>
<NewExpression>
<MemberExpression>
<PrimaryExpression>
<TokenNode Value="5" Line="9" Column="32" />
</PrimaryExpression>
</MemberExpression>
</NewExpression>
</LeftHandSideExpression>
</PostfixExpression>
</UnaryExpression>
</MultiplicativeExpression>
</AdditiveExpression>
</ShiftExpression>
</RelationalExpression>
</EqualityExpression>
<TokenNode Value="===" Line="9" Column="34" />
<RelationalExpression>
<ShiftExpression>
<AdditiveExpression>
<MultiplicativeExpression>
<UnaryExpression>
<PostfixExpression>
<LeftHandSideExpression>
<NewExpression>
<MemberExpression>
<PrimaryExpression>
<TokenNode Value="0" Line="9" Column="38" />
</PrimaryExpression>
</MemberExpression>
</NewExpression>
</LeftHandSideExpression>
</PostfixExpression>
</UnaryExpression>
</MultiplicativeExpression>
</AdditiveExpression>
</ShiftExpression>
</RelationalExpression>
</EqualityExpression>
</BitwiseANDExpression>
</BitwiseXORExpression>
</BitwiseORExpression>
</LogicalANDExpression>
</LogicalORExpression>
</ConditionalExpression>
</AssignmentExpression>
</Expression>
最佳答案
如果您想编写不需要列出所有联合情况的通用联合处理代码，那么您可能需要使用 F# 反射 API。这是一个简单的例子。formatUnion函数使用 F# 反射。它假定类型参数 'T是联合类型并使用 GetUnionFields获取包含当前案例名称和参数的元组。它打印当前案例名称并遍历所有参数。如果某些参数是类型 'T 的值(意味着它是递归联合)，我们递归打印有关该值的信息:
let rec formatUnion indent (value:'T) = //'
// Get name and arguments of the current union case
let info, args = Reflection.FSharpValue.GetUnionFields(value, typeof<'T>) //'
// Print current name (with some indentation)
printfn "%s%s" indent info.Name
for a in args do
match box a with
| :? 'T as v ->
// Recursive use of the same union type..
formatUnion (indent + " ") v
| _ -> ()
以下示例在一个非常简单的联合值上运行该函数:
type Element = | Nil | And of Element * Element | Or of Element * Element
formatUnion "" (And(Nil, Or(Nil, Nil)))
// Here is the expected output:
// And
// Nil
// Or
// Nil
// Nil
作为旁注，我认为您可以通过为
BinaryOperator 提供案例来大大简化您的歧视联合。和 UnaryOperator (带有一个附加参数)而不是明确列出所有元素类型。那么你可能可以直接实现该功能，因为它会非常简单。就像是:type BinaryOperator = LogicalOr | LogicalAnd | BitwiseOr // ...
type UnaryOperator = Statement | Block | Initializer // ...
type Element =
| BinaryOperator of BinaryOperator * Element * Element
| UnaryOperator of UnaryOperator * Element
关于f# - 如何将大型可区分联合树转换为可读形式？，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/3817819/