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Ada solution added
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If there is more then one occurrence then return smallest i such that haystack[i] = needle.
=={{header|Ada}}==
<ada>
with Ada.Strings.Unbounded; use Ada.Strings.Unbounded;
with Ada.Text_IO; use Ada.Text_IO;
procedure Test_List_Index is
Not_In : exception;
type List is array (Positive range <>) of Unbounded_String;
function Index (Haystack : List; Needle : String) return Positive is
begin
for Index in Haystack'Range loop
if Haystack (Index) = Needle then
return Index;
end if;
end loop;
raise Not_In;
end Index;
-- Functions to create lists
function "+" (X, Y : String) return List is
begin
return (1 => To_Unbounded_String (X), 2 => To_Unbounded_String (Y));
end "+";
function "+" (X : List; Y : String) return List is
begin
return X & (1 => To_Unbounded_String (Y));
end "+";
Haystack : List := "Zig"+"Zag"+"Ronald"+"Bush"+"Krusty"+"Wally"+"Charlie"+"Bush"+"Bozo";
procedure Check (Needle : String) is
begin
Put (Needle);
Put_Line ("at" & Positive'Image (Index (Haystack, Needle)));
exception
when Not_In => Put_Line (" is not in");
end Check;
begin
Check ("Washington");
Check ("Bush");
end Test_List_Index;
</ada>
Sample output:
<pre>
Washington is not in
Bushat 4
</pre>
=={{header|ALGOL 68}}==
FORMAT hay stack := $c("Zig","Zag","Ronald","Bush","Krusty","Wally","Charlie","Bush","Bozo")$;
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