Make directory path

There is a built-in function for this:

mkdir 'path/to/dir'

Alternatively, a custom solution (as per task description) that only uses the built-in mkdir non-recursively. The "triangle reduce" meta-operator [\ ] is used get the intermediate results of a left fold with the comma operator on the list of path elements.

for [\,] $*SPEC.splitdir("../path/to/dir") -> @path {
    mkdir $_ unless .e given $*SPEC.catdir(@path).IO;
}