Mihaela Mihaljevic
69678d31a1
Add the EXSLT common/math/sets modules, dispatched by resolving a function's prefix to its namespace (FunctionTable.call falls back to namespace lookup), so any prefix bound to an EXSLT namespace works. math:min/max/highest/lowest/ abs/sqrt (with the NaN rule), set:distinct/difference/intersection/ has-same-node/leading/trailing (by node identity and document order), and exsl:object-type. math:power and the transcendentals are omitted (they need a C math library the Foundation-free target excludes); exsl:node-set awaits result-tree-fragment support. Part of #105 (Tier 3)
74 lines
3.2 KiB
Swift
74 lines
3.2 KiB
Swift
extension PureXML.XPath {
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/// One XPath function: it receives its already-evaluated argument values and
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/// the evaluation context, and returns a value.
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typealias FunctionImplementation = (_ arguments: [Value], _ context: EvaluationContext) throws -> Value
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/// The evaluation context an expression is evaluated against: the context
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/// node, its position and size within the current node-set, the variable
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/// bindings, and the function library. Predicates and the `position()` and
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/// `last()` functions read the position and size.
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struct EvaluationContext {
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var node: Node
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var position: Int
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var size: Int
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var variables: [String: Value]
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var functions: FunctionTable
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/// Prefix-to-URI bindings supplied at evaluation time, so a name test like
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/// `x:foo` resolves `x` to a URI and matches by namespace rather than by the
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/// document's own prefix. Empty by default, in which case matching falls
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/// back to the in-document prefix string.
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var namespaces: [String: String] = [:]
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/// A copy positioned on `node` at one-based `position` within a node-set of
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/// `size`, keeping the same variables, functions, and namespace bindings.
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func focused(on node: Node, position: Int, size: Int) -> EvaluationContext {
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EvaluationContext(
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node: node,
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position: position,
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size: size,
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variables: variables,
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functions: functions,
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namespaces: namespaces,
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)
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}
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}
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/// The XPath function library: a name-to-implementation table. The core set is
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/// built in; further functions extend it.
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struct FunctionTable {
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private var table: [String: FunctionImplementation]
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init(_ table: [String: FunctionImplementation] = [:]) {
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self.table = table
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}
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/// Returns a table with `implementation` registered under `name`.
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func adding(_ name: String, _ implementation: @escaping FunctionImplementation) -> FunctionTable {
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var copy = table
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copy[name] = implementation
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return FunctionTable(copy)
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}
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/// Merges another table's entries over this one's.
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func merging(_ other: FunctionTable) -> FunctionTable {
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FunctionTable(table.merging(other.table) { _, new in new })
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}
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func call(_ name: String, _ arguments: [Value], _ context: EvaluationContext) throws -> Value {
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if let implementation = table[name] {
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return try implementation(arguments, context)
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}
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// A prefixed name may be an EXSLT extension function: resolve the prefix
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// to its namespace URI and dispatch by namespace.
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if let colon = name.firstIndex(of: ":") {
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let prefix = String(name[..<colon])
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let local = String(name[name.index(after: colon)...])
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if let uri = context.namespaces[prefix], let implementation = EXSLT.implementation(uri: uri, local: local) {
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return try implementation(arguments, context)
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}
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}
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throw QueryError.unknownFunction(name)
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}
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}
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}
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