Scoping in Modules Tree
In this chapter the main running program will be referred to as the program and subsequent modules will be referred to as modules. With this definition, every Tyl application is composed of program and modules. running the application means running the program, that will run all subsequent modules according to their appearance order in the code.

With this in mind let's start with an app program and app.data and app.func modules:

First, app.data is run and pi is assigned value 3.1416, then app.func is run and area function is declared. Though pi is not in app.func tree, it will be seen by area function, because pi is a global variable of app.data and essentially of app iteself. In this case app.data acts as application repository and holds all application data that is used by the program and all modules. so in line print 'pi is ' + pi, pi will have already its value, and it will be printed.

Flipping modules call order, and updating app.func:

Line print '[app.func] pi is ' + pi, will be the first statement that will be run, so pi will be declared with a value of NULL. The next statement that will be run is pi 3.1416 which will be merely a variable assignment. In order to avoid such errors it is needed to call the modules in an order that for each running statement, its variables are defined properly on the spot or are already defined.

Variables that are not global behave the same as described in variables scope page, regrading to their containing module.
Module Location Search & Relative Paths
All the above program and modules where on the same directory 'app', therefore the plain call #mod app.data, casused the system to look for file 'app.data.tyl' in the same directory that the calling module 'app.tyl' resides. plain call means that the relative path of the module in the calling statement is not relative, but merely a file name, with or without the file extention.

Examples of module relative paths:
! examples of module calls, and the way their relative
! paths are written. in all calls except the first call
! the extention '.tyl' is omitted
! if the relative path has spaces, it must be enclose
! in quotation marks (')
! 'app.tyl' in full path (without spaces, with file extention)
#mod C:/tylprojects/app/app.tyl
! 'app.tyl' in full path (with spaces, without file extention)
#mod 'C:/tylprojects/happy app/app'
! 'app.tyl' in adjacent directory 'app2'
#mod ../app2/app
! 'app.tyl' in other relative directory (with spaces)
#mod '../../web apps/app'
! 'textmod.tyl' in the current working directory or in
! global modules repository
#mod textmod
! 'happy mod.tyl' in the current working directory or in
! global modules repository (with spaces)
#mod 'happy mod'

This is a scenario of a plain call to a global module 'textmod.tyl':

In line #mod textmod, Tyl system will search for file 'textmod.tyl' in directory 'app', if not found it will look for it in Tyl global modules reository.