com.livecode.list: Add "index of _ in _" accessor.

peter-b · peter-b · commit bc3a548b9aa7 · 2015-03-06T10:18:28.000Z
Add a new operation on lists:

    the index of &lt;tNeedle&gt; in &lt;tList&gt;

which returns the 1-based index of the first element in &lt;tList&gt; that
is equal to &lt;tNeedle&gt;, or 0 if no element of &lt;tList&gt; is equal to
&lt;tNeedle&gt;.

There are two variants of the operation:

    the first index of &lt;tNeedle&gt; in &lt;tList&gt;
    the last index of &lt;tNeedle&gt; in &lt;tList&gt;

If &lt;tNeedle&gt; is a list, it is considered as an element of &lt;tList&gt; not
as a subsequence of &lt;tList&gt;.
diff --git a/libscript/src/list.mlc b/libscript/src/list.mlc
@@ -74,6 +74,8 @@ public foreign handler MCListExecDeleteElementRangeOf(in Start as LCIndex, in Fi
 public foreign handler MCListExecDeleteFirstElementOf(inout Target as List) as undefined binds to "<builtin>"
 public foreign handler MCListExecDeleteLastElementOf(inout Target as List) as undefined binds to "<builtin>"
 
+public foreign handler MCListEvalIndexOfElement(in IsLast as CBool, in Needle as any, in Haystack as List, out Index as LCUIndex) as undefined binds to "<builtin>"
+
 --
 
 /*
@@ -855,4 +857,40 @@ begin
     MCListRepeatForEachElement(iterator, Iterand, container)
 end syntax
 
+----------------------------------------------------------------
+
+/*
+Summary:	Find the first or last occurrence of <Needle> within <Haystack>
+
+Needle:	An expression which evaluates to any value.
+Target:	An expression which evaluates to a list.
+
+Returns:	Returns the index from the start of <Haystack>.
+
+Example:
+	variable tVar as List
+	variable tOffset as Number
+	put ["a", "b", "c", "d", "b"]
+	put the index of "b" in tVar into tOffset
+	-- tOffset contains 2
+
+	put the last index of "b" in tVar into tOffset
+	-- tOffset contains 5
+
+Description:
+Use `the index of` to find where particular elements occur within a
+list.  <Haystack> is scanned for an element that is equal to <Needle>,
+and the position of the element found is returned.  If neither the
+"first index" nor "last index" are specified, the index of the first
+element found is returned.  If no element of <Haystack> is equal to
+<Needle>, the return value is 0.
+
+Tags: Lists
+*/
+syntax ListIndex is prefix operator with precedence 1
+	"the" ( "first" <IsLast=false> | "last" <IsLast=true> | <IsLast=false> ) "index" "of" <Needle: Expression> "in" <Haystack: Expression>
+begin
+	MCListEvalIndexOfElement(IsLast, Needle, Haystack, output)
+end syntax
+
 end module
diff --git a/libscript/src/module-list.cpp b/libscript/src/module-list.cpp
@@ -441,6 +441,46 @@ extern "C" MC_DLLEXPORT void MCListEvalIsNotEqualTo(MCProperListRef p_left, MCPr
     r_output = !MCProperListIsEqualTo(p_left, p_right);
 }
 
+////////////////////////////////////////////////////////////////
+
+static void
+MCListEvalIndexOfElementInRange (bool p_is_last,
+                                 MCValueRef p_needle,
+                                 MCProperListRef p_haystack,
+                                 MCRange p_range,
+                                 uindex_t & r_output)
+{
+	if (MCProperListIsEmpty (p_haystack))
+	{
+		r_output = 0;
+		return;
+	}
+
+	uindex_t t_offset = 0;
+	bool t_found = false;
+	if (!p_is_last)
+		t_found = MCProperListFirstIndexOfElementInRange (p_haystack, p_needle,
+		                                                  p_range, t_offset);
+	else
+		t_found = MCProperListLastIndexOfElementInRange (p_haystack, p_needle,
+		                                                 p_range, t_offset);
+
+	if (t_found)
+		r_output = t_offset + 1;
+	else
+		r_output = 0;
+}
+
+extern "C" MC_DLLEXPORT void
+MCListEvalIndexOfElement (bool p_is_last,
+                          MCValueRef p_needle,
+                          MCProperListRef p_haystack,
+                          uindex_t & r_output)
+{
+	MCRange t_range = MCRangeMake (0, UINDEX_MAX);
+	MCListEvalIndexOfElementInRange (p_is_last, p_needle, p_haystack, t_range, r_output);
+}
+
 ////////////////////////////////////////////////////////////////////////////////////////////////////
 
 #ifdef _TEST
diff --git a/tests/lcb/stdlib/list.lcb b/tests/lcb/stdlib/list.lcb
@@ -376,4 +376,20 @@ public handler TestRepeatElement()
 	test "repeat element (count)" when tCount is 4
 end handler
 
+----------------------------------------------------------------
+
+public handler TestIndex()
+	variable t
+	put ["x", 1, true, [], []] into t
+
+	test "index" when the index of 1 in t is 2
+	test "index (list)" when the index of [] in t is 4
+	test "index (missing)" when the index of false in t is 0
+
+	test "first index" when the first index of [] in t is 4
+	test "last index" when the last index of [] in t is 5
+
+	test "index (empty)" when the index of 1 in [] is 0
+end handler
+
 end module
