Transcript REBOL 2, Lists

REBOL
Lists
REBOL does it differently
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Other languages:
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Lists (and similar sequences) are singly-linked
head returns the first element of the series
tail returns the remainder of the series, minus the head
REBOL:
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Series are doubly-linked, hence traversable in either direction
Any reference to a series is a reference to some position in the
series
head returns the beginning of the series
tail returns the end of the series
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Traversing a sequence
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head returns the beginning of the sequence
tail returns the end of the sequence
next returns the next position in the sequence
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back returns the previous position in the sequence
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If already at the tail, returns the tail
If already at the head, returns the head
head? tests if a position is the beginning of a sequence
tail? tests if a position is the end of a sequence
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Example traversals
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>>
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>>
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>>
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str: "REBOL"
"REBOL"
mid: next next str
"BOL"
head? mid
false
head mid
"REBOL"
end: tail str
""
back end
"L"
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Getting elements from a sequence
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>>
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str: "REBOL"
"REBOL"
first str
#"R"
second str
#"E"
last str
#"L"
pick str 4
#"O"
pick str 8
none
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Indexing into a sequence
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>>
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str: "REBOL"
"REBOL"
index? str
1
mid: at str 3
"BOL"
at mid 2
"OL”
at mid -1
"EBOL"
index? at mid -1
2
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The End
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