Loop, string chars. While F# programs can use many advanced features, often they need to perform simpler tasks like looping over a string. This can be done in many ways in F#.
Version 3 We can iterate over indexes, and then access each char by index, with a for-to loop.
Version 4 It is possible to access the characters from the string with the Chars accessor.
Version 5 For a reverse loop with indexes, we can use for downto—this is a decrementing index loop.
let value = "abc"// Version 1: use for-in.
for c in value do
printfn $"For-in: {c}"// Version 2: use for-in with Seq.rev for reverse loop.
for c in Seq.rev value do
printfn $"Seq.rev: {c}"// Version 3: use for-to loop.
for i = 0 to value.Length - 1 do
let c = value[i]
printfn $"For-to []: {c}"// Version 4: Use for-to loop with Chars.
for i = 0 to value.Length - 1 do
let c = value.Chars(i)
printfn $"For-to Chars: {c}"// Version 5: use for-downto loop for reverse loop.
for i = value.Length - 1 downto 0 do
let c = value[i]
printfn $"For-downto: {c}"For-in: a
For-in: b
For-in: c
Seq.rev: c
Seq.rev: b
Seq.rev: a
For-to []: a
For-to []: b
For-to []: c
For-to Chars: a
For-to Chars: b
For-to Chars: c
For-downto: c
For-downto: b
For-downto: a
Summary. Looping is often done in F#, and looping over strings is a common requirement as well. With for-in and for-to, we have a variety of powerful loops to choose from.
Dot Net Perls is a collection of tested code examples. Pages are continually updated to stay current, with code correctness a top priority.
Sam Allen is passionate about computer languages. In the past, his work has been recommended by Apple and Microsoft and he has studied computers at a selective university in the United States.
