Add isletter (#542)

Author: jmkuhn

README.md

@@ -403,6 +403,8 @@ Currently, the `@compat` macro supports the following syntaxes:
 * `isupper`, `islower`, `ucfirst` and `lcfirst` are now `isuppercase`, `islowercase`,
   `uppercasefirst` and `lowercasefirst` ([#26442]).
 
+* `isalpha` is now `isletter` ([#27077]).
+
 ## New macros
 
 * `@__DIR__` has been added ([#18380])
@@ -626,3 +628,4 @@ includes this fix. Find the minimum version from there.
 [#26442]: https://github.com/JuliaLang/julia/issues/26442
 [#26660]: https://github.com/JuliaLang/julia/issues/26660
 [#26670]: https://github.com/JuliaLang/julia/issues/26670
+[#27077]: https://github.com/JuliaLang/julia/issues/27077

src/Compat.jl

@@ -1842,6 +1842,12 @@ else
     using LinearAlgebra: qr
 end
 
+# https://github.com/JuliaLang/julia/pull/27077
+@static if VERSION < v"0.7.0-DEV.5087"
+    export isletter
+    const isletter = isalpha
+end
+
 include("deprecated.jl")
 
 end # module Compat

test/runtests.jl

@@ -1727,4 +1727,9 @@ let A = [1 2; 1 2; 1 2]
     @test f[1] * [f[2]; [0 0]] ≈ A[:,f[3]]
 end
 
+# 0.7.0-DEV.5087
+@test isletter('a')
+@test isletter('β')
+@test !isletter('3')
+
 nothing