20 lines
553 B
OCaml
20 lines
553 B
OCaml
(* Purely functional queues based on a pair of lists *)
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type 'a t = {rear: 'a list; front: 'a list}
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let empty = {rear=[]; front=[]}
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let enq x q = {q with rear = x::q.rear}
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let rec deq = function
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{rear=[]; front= []} -> None
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| {rear; front= []} -> deq {rear=[]; front = List.rev rear}
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| {rear; front=x::f} -> Some ({rear; front=f}, x)
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let rec peek = function
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{rear=[]; front= []} -> None
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| {rear; front= []} -> peek {rear=[]; front = List.rev rear}
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| {rear=_; front=x::_} as q -> Some (q,x)
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let is_empty q = (q = empty)
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