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peter-bpeter-b
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com.livecode.list: Add "offset of _ in _" accessor.
 Add a new operation on lists: the offset of <tNeedle> in <tList> which returns the 1-based index of the start of the first subsequence in <tList> that is equal to <tNeedle>, or 0 if no subsequence of <tList> is equal to <tNeedle>. There are two variants of the operation: the first offset of <tNeedle> in <tList> the last offset of <tNeedle> in <tList> <tNeedle> must be a List.
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Lines changed: 99 additions & 0 deletions

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‎libscript/src/list.mlc‎

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@@ -78,6 +78,8 @@ public foreign handler MCListEvalIndexOfElement(in IsLast as CBool, in Needle as
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public foreign handler MCListEvalIndexOfElementAfter(in IsLast as CBool, in Needle as any, in After as LCIndex, in Haystack as List, out Index as LCUIndex) as undefined binds to "<builtin>"
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public foreign handler MCListEvalIndexOfElementBefore(in IsLast as CBool, in Needle as any, in Before as LCIndex, in Haystack as List, out Index as LCUIndex) as undefined binds to "<builtin>"
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public foreign handler MCListEvalOffsetOfList(in IsLast as CBool, in Needle as List, in Haystack as List, out Index as LCUIndex) as undefined binds to "<builtin>"
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--
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/*
@@ -964,4 +966,41 @@ begin
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MCListEvalIndexOfElementBefore(IsLast, Needle, Before, Haystack, output)
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end syntax
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----------------------------------------------------------------
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/*
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Summary: Find the first or last occurrence of <Needle> within <Haystack>
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Needle: An expression which evaluates to a list.
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Target: An expression which evaluates to a list.
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Returns: Returns the index from the start of <Haystack>.
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Example:
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variable tVar as List
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variable tOffset as Number
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put ["a", "b", "c", "d", "b", "c"]
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put the offset of ["b","c"] in tVar into tOffset
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-- tOffset contains 2
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put the last offset of ["b", "c"] in tVar into tOffset
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-- tOffset contains 5
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Description:
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Use `the offset of` to find where a particular sub-list occurs within
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a list. <Haystack> is scanned for a sequence of elements that are
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equal to the elements of <Needle>, and the position of the start of
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the sequence found is returned. If neither the "first offset" nor
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"last offset" are specified, the index of the first matching seb-list
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found is returned. If no sub-list of <Haystack> is equal to <Needle>,
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the return value is 0.
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Tags: Lists
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*/
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syntax ListOffset is prefix operator with precedence 1
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"the" ( "first" <IsLast=false> | "last" <IsLast=true> | <IsLast=false> ) "offset" "of" <Needle: Expression> "in" <Haystack: Expression>
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begin
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MCListEvalOffsetOfList(IsLast, Needle, Haystack, output)
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end syntax
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end module

‎libscript/src/module-list.cpp‎

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@@ -527,6 +527,46 @@ MCListEvalIndexOfElementBefore (bool p_is_last,
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r_output);
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}
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////////////////////////////////////////////////////////////////
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static void
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MCListEvalOffsetOfListInRange (bool p_is_last,
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MCProperListRef p_needle,
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MCProperListRef p_haystack,
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MCRange p_range,
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uindex_t & r_output)
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{
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if (MCProperListIsEmpty (p_haystack))
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{
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r_output = 0;
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return;
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}
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uindex_t t_offset = 0;
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bool t_found = false;
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if (!p_is_last)
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t_found = MCProperListFirstOffsetOfListInRange (p_haystack, p_needle,
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p_range, t_offset);
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else
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t_found = MCProperListLastOffsetOfListInRange (p_haystack, p_needle,
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p_range, t_offset);
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if (t_found)
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r_output = t_offset + 1;
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else
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r_output = 0;
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}
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extern "C" MC_DLLEXPORT void
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MCListEvalOffsetOfList (bool p_is_last,
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MCProperListRef p_needle,
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MCProperListRef p_haystack,
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uindex_t & r_output)
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{
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MCRange t_range = MCRangeMake (0, UINDEX_MAX);
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MCListEvalOffsetOfListInRange (p_is_last, p_needle, p_haystack, t_range, r_output);
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}
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////////////////////////////////////////////////////////////////////////////////////////////////////
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#ifdef _TEST

‎tests/lcb/stdlib/list.lcb‎

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@@ -545,4 +545,24 @@ public handler TestIndexBeforeZero()
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test "last index before (+ve, 0)" when the last index of true before 0 in t is tNoBefore
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end handler
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----------------------------------------------------------------
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-- Finding subsequence offsets
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----------------------------------------------------------------
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public handler TestOffset()
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variable t
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put ["x", 1, true, [], []] into t
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test "offset" when the offset of [1, true] in t is 2
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test "offset (missing)" when the offset of [true, 1] in t is 0
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test "offset (missing, overlap start)" when the offset of [false, "x"] in t is 0
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test "offset (missing, overlap end)" when the offset of [[], [], false] in t is 0
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test "first offset" when the first offset of [[]] in t is 4
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test "last offset" when the last offset of [[]] in t is 5
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test "offset (empty)" when the offset of [] in t is 0
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end handler
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end module

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