ml
87 lines
2.3 KiB
Go
87 lines
2.3 KiB
Go
package interpreters
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// Predicate is a function that specifies whether a certain description
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// is active within another.
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type Predicate func(inst *Instance) bool
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// Always is a predicate that returns true for every call.
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func Always(inst *Instance) bool {
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return true
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}
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// Never is a predicate that returns false for every call.
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func Never(inst *Instance) bool {
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return false
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}
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// Description is the meta information about a data interpreter. A description
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// is an immutable object that provides new descriptions with any modification.
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type Description struct {
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fields map[string]*entry
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refinements map[string]*refinement
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lastField *entry
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}
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var empty = newDescription()
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// New returns an empty description.
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func New() *Description {
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return empty
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}
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func newDescription() *Description {
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return &Description{
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fields: make(map[string]*entry),
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refinements: make(map[string]*refinement)}
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}
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func (desc *Description) clone() *Description {
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cloned := newDescription()
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for key, e := range desc.fields {
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cloned.fields[key] = e
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}
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for key, r := range desc.refinements {
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cloned.refinements[key] = r
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}
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return cloned
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}
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// For returns an instance of an interpreter with the given data slice
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// as backing buffer.
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func (desc *Description) For(data []byte) *Instance {
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return &Instance{desc: desc, data: data}
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}
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// With extends the given description with a new field.
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// The returned description is a new, separated object from the originating one.
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func (desc *Description) With(key string, byteStart int, byteCount int) *Description {
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cloned := desc.clone()
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cloned.lastField = &entry{start: byteStart, count: byteCount}
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cloned.fields[key] = cloned.lastField
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return cloned
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}
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// As sets the value range for the previously added field.
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func (desc *Description) As(fieldRange FieldRange) *Description {
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if desc.lastField == nil {
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panic("No field active")
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}
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desc.lastField.via = fieldRange
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return desc
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}
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// Refining adds another description within the given one. The provided predicate
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// determines whether the refined description is active.
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func (desc *Description) Refining(key string, byteStart int, byteCount int, refined *Description, predicate Predicate) *Description {
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cloned := desc.clone()
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cloned.refinements[key] = &refinement{
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entry: entry{start: byteStart, count: byteCount},
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desc: refined,
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predicate: predicate}
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return cloned
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}
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