Szathmáry László honlapja @ DEIK | Nim2 / Check if a text is ASCII only

We have a text and we want to test if it consists of ASCII characters only.

import std/sequtils # all
import std/unicode # Rune

func isAscii(c: char): bool =
ord(c) < 128

func isAscii(r: Rune): bool =
ord(r) < 128

func isAscii(s: string): bool =
s.all(isAscii)

let
s1 = "hello world 2026"
s2 = "László"
c1 = 'a'
c2 = "é".runeAt(0)
c3 = "a".runeAt(0)

echo s1.isAscii # true
echo s2.isAscii # false
echo c1.isAscii # true
echo c2.isAscii # false
echo c3.isAscii # true

You can also join the first two functions:

func isAscii(c: char | Rune): bool =
ord(c) < 128

func isAscii(s: string): bool =
s.all(isAscii)

Now the first function is a generic function. Actually, it's just syntactic sugar for the longer form:

func isAscii[T: char | Rune](c: T): bool =
ord(c) < 128

The compiler generates a separate instantiation for each concrete type it's called with. It's fully statically typed and it has zero-overhead at runtime.