com.livecode.list: Add "offset of _ before _ in _" accessor.

peter-b · peter-b · commit 1f4dd2f6a760 · 2015-03-06T13:06:02.000Z
Add a new operation on lists:
    
   the offset of &lt;tNeedle&gt; before &lt;tPosition&gt; in &lt;tList&gt;
    
This looks for an subsequence equal to &lt;tNeedle&gt; in the subsequence of
&lt;tList&gt; ending at the 1-based index &lt;tPosition&gt; (exclusive).  It
returns the 1-based index in &lt;tList&gt; of the first element of the
matching subsequence, or 0 if no matching subsequence is found.
    
There are two variants of the operation:
    
    the first offset of &lt;tNeedle&gt; before &lt;tPosition&gt; in &lt;tList&gt;
    the last offset of &lt;tNeedle&gt; before &lt;tPosition&gt; in &lt;tList&gt;
    
&lt;tNeedle&gt; must be a List.
diff --git a/libscript/src/list.mlc b/libscript/src/list.mlc
@@ -80,6 +80,7 @@ public foreign handler MCListEvalIndexOfElementBefore(in IsLast as CBool, in Nee
 
 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>"
 public foreign handler MCListEvalOffsetOfListAfter(in IsLast as CBool, in Needle as List, in After as LCIndex, in Haystack as List, out Index as LCUIndex) as undefined binds to "<builtin>"
+public foreign handler MCListEvalOffsetOfListBefore(in IsLast as CBool, in Needle as List, in Before as LCIndex, in Haystack as List, out Index as LCUIndex) as undefined binds to "<builtin>"
 
 --
 
@@ -1043,4 +1044,41 @@ begin
 	MCListEvalOffsetOfListAfter(IsLast, Needle, After, Haystack, output)
 end syntax
 
+/*
+Summary:	Find the first or last occurrence of <Needle> within the head of <Haystack>
+
+Needle:	An expression which evaluates to List.
+Before:	An expression which evaluates to a valid index in Target.
+Target:	An expression which evaluates to a List.
+
+Returns:	Returns the index in <Haystack>.
+
+Example:
+	variable tVar as List
+	variable tOffset as Number
+	put ["a", "b", "c", "d", "b","c"]
+	put the offset of ["b","c"] before 5 in tVar into tOffset
+	--tOffset contains 2
+
+	put the first offset of ["b","c"] before 6 in tVar into tOffset
+	--tOffset contains 2
+
+Description:
+
+Use `the offset of… before` to find where a particular sub-list occurs
+within a list.  <Haystack> is scanned for a sequence of elements that
+are equal to the elements of <Needle>, stopping before the position
+<Before>, and the position of the start of the sequence found is
+returned.  If no sub-list of <Haystack> before the position <Before>
+is equal to <Needle>, the return value is 0.  If neither "first" nor
+"last" is specified, the last matching subsequence is found.
+
+Tags: Lists
+*/
+syntax ListOffsetBefore is prefix operator with precedence 1
+	"the" ( "first" <IsLast=false> | "last" <IsLast=true> | <IsLast=true> ) "offset" "of" <Needle: Expression> "before" <Before: Expression> "in" <Haystack: Expression>
+begin
+	MCListEvalOffsetOfListBefore(IsLast, Needle, Before, Haystack, output)
+end syntax
+
 end module
diff --git a/libscript/src/module-list.cpp b/libscript/src/module-list.cpp
@@ -589,6 +589,30 @@ MCListEvalOffsetOfListAfter (bool p_is_last,
 	                               r_output);
 }
 
+extern "C" MC_DLLEXPORT void
+MCListEvalOffsetOfListBefore (bool p_is_last,
+                              MCProperListRef p_needle,
+                              index_t p_before,
+                              MCProperListRef p_haystack,
+                              uindex_t & r_output)
+{
+	uindex_t t_start, t_count;
+	if (p_before == 0)
+	{
+		t_start = UINDEX_MAX;
+	} else if (!MCChunkGetExtentsOfElementChunkByExpressionInRange (p_haystack,
+	                nil, p_before, true, false, true, t_start, t_count))
+	{
+		MCErrorCreateAndThrow (kMCGenericErrorTypeInfo, "reason",
+		                       MCSTR("chunk index out of range"), nil);
+		return;
+	}
+
+	MCListEvalOffsetOfListInRange (p_is_last, p_needle, p_haystack,
+	                               MCRangeMake(0, t_start),
+	                               r_output);
+}
+
 ////////////////////////////////////////////////////////////////////////////////////////////////////
 
 #ifdef _TEST
diff --git a/tests/lcb/stdlib/list.lcb b/tests/lcb/stdlib/list.lcb
@@ -639,5 +639,80 @@ public handler TestOffsetAfterZero()
 	test "last offset after (+ve, 0)" when the last offset of [true,false] after 0 in t is tNoAfter
 end handler
 
+----------------------------------------------------------------
+
+handler TestOffsetBefore_InvalidPositive()
+	return the offset of [true] before 3 in [true]
+end handler
+handler TestOffsetBefore_InvalidNegative()
+	return the offset of [true] before -2 in [true]
+end handler
+handler TestFirstOffsetBefore_InvalidPositive()
+	return the first offset of [true] before 3 in [true]
+end handler
+handler TestFirstOffsetBefore_InvalidNegative()
+	return the first offset of [true] before -2 in [true]
+end handler
+handler TestLastOffsetBefore_InvalidPositive()
+	return the last offset of [true] before 3 in [true]
+end handler
+handler TestLastOffsetBefore_InvalidNegative()
+	return the last offset of [true] before -2 in [true]
+end handler
+public handler TestOffsetBefore()
+	variable t
+	put [true, false, true, true, false] into t
+
+	test "offset before (+ve)" when the offset of [true,false] before 4 in t is 1
+	test "offset before (-ve)" when the offset of [true,false] before -2 in t is 1
+	test "offset before (+ve, limit)" when the offset of [true,false] before 6 in t is 4
+	test "offset before (+ve, missing)" when the offset of [false,true] before 2 in t is 0
+	test "offset before (-ve, missing)" when the offset of [false,true] before -4 in t is 0
+
+	MCUnitTestHandlerThrows(TestOffsetBefore_InvalidPositive, "offset before (+ve, invalid)")
+	MCUnitTestHandlerThrows(TestOffsetBefore_InvalidNegative, "offset before (-ve, invalid)")
+end handler
+public handler TestFirstOffsetBefore()
+	variable t
+	put [true, false, true, true, false] into t
+
+	test "first offset before (+ve)" when the first offset of [true,false] before 5 in t is 1
+	test "first offset before (-ve)" when the first offset of [true,false] before -1 in t is 1
+	test "first offset before (+ve, limit)" when the first offset of [true,false] before 6 in t is 1
+	test "first offset before (+ve, missing)" when the first offset of [false,true] before 2 in t is 0
+	test "first offset before (-ve, missing)" when the first offset of [false,true] before -4 in t is 0
+
+	MCUnitTestHandlerThrows(TestFirstOffsetBefore_InvalidPositive, "first offset before (+ve, invalid)")
+	MCUnitTestHandlerThrows(TestFirstOffsetBefore_InvalidNegative, "first offset before (-ve, invalid)")
+end handler
+public handler TestLastOffsetBefore()
+	variable t
+	put [true, false, true, true, false] into t
+
+	test "last offset before (+ve)" when the last offset of [true,false] before 4 in t is 1
+	test "last offset before (-ve)" when the last offset of [true,false] before -2 in t is 1
+	test "last offset before (+ve, limit)" when the last offset of [true,false] before 6 in t is 4
+	test "last offset before (+ve, missing)" when the last offset of [false,true] before 2 in t is 0
+	test "last offset before (-ve, missing)" when the last offset of [false,true] before -4 in t is 0
+
+	MCUnitTestHandlerThrows(TestLastOffsetBefore_InvalidPositive, "last offset before (+ve, invalid)")
+	MCUnitTestHandlerThrows(TestLastOffsetBefore_InvalidNegative, "last offset before (-ve, invalid)")
+end handler
+public handler TestOffsetBeforeZero()
+	-- "offset of _ before 0 in _" should be equivalent to "last offset of _ in _"
+	variable t
+	put [true, false, true, true, false] into t
+	variable tNoBefore
+
+	put the last offset of [true,false] in t into tNoBefore
+	test "offset before (+ve, 0)" when the offset of [true,false] before 0 in t is tNoBefore
+
+	put the first offset of [true,false] in t into tNoBefore
+	test "first offset before (+ve, 0)" when the first offset of [true,false] before 0 in t is tNoBefore
+
+	put the last offset of [true,false] in t into tNoBefore
+	test "last offset before (+ve, 0)" when the last offset of [true,false] before 0 in t is tNoBefore
+end handler
+
 
 end module
