sclass VStack implements Steppable { new L<Computable> stack; O latestResult; // was last instruction a return? // can be used by computations to switch without a label transient bool justReturned; transient O subComputationResult; // the null sentinel replaces a null function result // when stored in latestResult sclass NullSentinel {} static new NullSentinel nullSentinel; *() {} *(Computable computation) { push(computation); } *(Iterable<Computable> l) { pushAll(l); } // A is what the function returns interface Computable<A> { public void step(VStack stack, O subComputationResult); } private O deSentinel(O o) { ret o instanceof NullSentinel ? null : o; } private O sentinel(O o) { ret o == null ? nullSentinel : o; } // called by computations or users to start a subroutine void push aka call(Computable computation) { stack.add(computation); } // perform a computation step. returns false iff done public bool step() { if (empty(stack)) false; justReturned = latestResult != null; subComputationResult = deSentinel(latestResult); latestResult = null; last(stack).step(this, subComputationResult); subComputationResult = null; true; } // called from a computation to return a value void _return(O value default null) { latestResult = sentinel(value); removeLast(stack); } // called from a computation to tail-call another routine void tailCall aka replace(Computable computation) { removeLast(stack); stack.add(computation); } // all-in-one evaluation function - call on an empty stack <A> A compute(Computable<A> computation) { if (computation == null) null; push(computation); stepAll(this); ret (A) latestResult; } // return result of just completed computation O result aka subResult() { ret deSentinel(latestResult); } bool hasSubResult() { ret justReturned; } void pushAll(Iterable<Computable> l) { fOr (Computable c : l) push(c); } }
Began life as a copy of #1030376
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Snippet ID: | #1030986 |
Snippet name: | VStack [backup before restructuring] |
Eternal ID of this version: | #1030986/1 |
Text MD5: | c9822bca9533b008cf477ebf9d8f4db2 |
Author: | stefan |
Category: | javax |
Type: | JavaX fragment (include) |
Public (visible to everyone): | Yes |
Archived (hidden from active list): | No |
Created/modified: | 2021-04-18 14:55:05 |
Source code size: | 2137 bytes / 79 lines |
Pitched / IR pitched: | No / No |
Views / Downloads: | 163 / 183 |
Referenced in: | -