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=={{header|Wren}}==

{{libheader|Wren-dynamic}}

<lang ecmascript>import "/dynamic" for Tuple

var Element = Tuple.create("Element", ["record", "index"])

var findFirst = Fn.new { |seq, pred|

var i = 0

for (e in seq) {

if (pred.call(e)) return Element.new(e, i)

i = i + 1

}

return Element.new(null, -1)

}

var City = Tuple.create("City", ["name", "pop"])

var cities = [

City.new("Lagos", 21.0),

City.new("Cairo", 15.2),

City.new("Kinshasa-Brazzaville", 11.3),

City.new("Greater Johannesburg", 7.55),

City.new("Mogadishu", 5.85),

City.new("Khartoum-Omdurman", 4.98),

City.new("Dar Es Salaam", 4.7),

City.new("Alexandria", 4.58),

City.new("Abidjan", 4.4),

City.new("Casablanca", 3.98)

]

var index = findFirst.call(cities) { |c| c.name == "Dar Es Salaam" }.index

System.print("Index of the first city whose name is 'Dar Es Salaam' is %(index).")

var city = findFirst.call(cities) { |c| c.pop < 5 }.record.name

System.print("First city whose population is less than 5 million is %(city).")

var pop = findFirst.call(cities) { |c| c.name[0] == "A" }.record.pop

System.print("The population of the first city whose name begins with 'A' is %(pop).")</lang>

{{out}}

<pre>

Index of the first city whose name is 'Dar Es Salaam' is 6.

First city whose population is less than 5 million is Khartoum-Omdurman.

The population of the first city whose name begins with 'A' is 4.58.

</pre>