39 lines
1.0 KiB
Go
39 lines
1.0 KiB
Go
package gonads
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// Thunk contains a partially computed value. This thunk is also lazy because
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// it will only run the underlying thunked action _once_ and then return the
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// result of that action, caching it for further use.
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//
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// If this is confusing to you, consider the following JavaScript:
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//
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// let add = (x, y) => x + y;
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// let addCurr = (x) => (y) => x + y;
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// console.log(add(2, 2)); // 4
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// console.log(addCurr(2)(2)); // 4
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// let addTwo = addCurr(2); // (y) => 2 + y;
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//
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// In this example, `addTwo` is a thunk that contains a partially applied addCurr
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// invocation.
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type Thunk[T any] struct {
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doer func() T // action being thunked
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o *Option[T] // cache for complete thunk data
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}
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// Force evaluates a Thunk's action if it needs to, otherwise it returns the
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// previously evaluated result.
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func (t Thunk[T]) Force() T {
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if t.o.IsSome() {
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return t.o.Yank()
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}
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t.o.Set(t.doer())
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return t.o.Yank()
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}
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func NewThunk[T any](doer func() T) *Thunk[T] {
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return &Thunk[T]{
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doer: doer,
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o: NewOption[T](),
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}
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}
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