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29 lines
525 B
R
29 lines
525 B
R
Stack <- setRefClass(
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'Stack',
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fields = list(
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.stack = 'list'
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),
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methods = list(
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push = function(obj) {
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.stack <<- c(.stack, list(obj))
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invisible(.self)
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},
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pop = function() {
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len <- length(.stack)
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if (len == 0)
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return(NULL)
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obj <- .stack[[len]]
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.stack <<- .stack[-len]
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obj
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},
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peek = function() {
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len <- length(.stack)
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if (len == 0) return(NULL)
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.stack[[len]]
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},
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size = function() {
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length(.stack)
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}
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)
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)
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