Introspection

Introspection
You are encouraged to solve this task according to the task description, using any language you may know.

This task asks to

• verify the version/revision of your currently running (compiler/interpreter/byte-compiler/runtime environment/whatever your language uses) and exit if it is too old.
• check whether the variable "bloop" exists and whether the math-function "abs()" is available and if yes compute abs(bloop).

Perl

Interpreter: Perl 5.x

require v5.6.1;    # run time version check
require 5.6.1;     # ditto
require 5.006_001; # ditto; preferred for backwards compatibility

Tcl

package require Tcl 8.2 ; # throws an error if older
if {[info exists bloop] && [llength [info functions abs]]} {
  puts [expr abs($bloop)]
}

E

def version := interp.getProps()["e.version"]

(There is no built-in version comparison, and the author of this example assumes that implementing a version comparison algorithm isn't the point of this task.)

escape fail {
    def &x := meta.getState().fetch("&bloop", fn { fail("no bloop") })
    if (!x.__respondsTo("abs", 0)) { fail("no abs") }
    x.abs()
}