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script:walkthrough:functions
Records 
 Scopes

Functions

A function is defined in the current scope using a def statement. def is a compound statement, so it must be either a single-line compound or end must be used in the end.

def func1(): pass

def func2()
end

The return statement is used to return a value from a function.

def func3(): return 'World'
print 'Hello', func3()

Arguments

Functions can be defined with a list of untyped arguments.

def func5(a, b, c)

Default values can be included.

def func5(a, b='default', c=100)

When calling a function, all arguments must have values. Argument names can always be included in the function call, regardless of whether they were defined with default values or not. When using names, the order can also be changed.

func5(c=5, a=100, b='OOO')

Records as arguments/return value

Records are passed by reference both in arguments and in the return value. This means that if a record is created as a local variable, it will be deleted even though it is returned.

def func4()
    record a          # 'a' owns the record
    a.value = "func4"
    return a          # non-owned reference returned
end
print func4().value   # throws NullError!

In this case, one could instead use the Record() function to return a copy of the record to the caller.

return Record(a)

When passing a record as argument, the function gets a non-owned reference.

record myrec
myrec.val = 'Original'
print myrec.val
def modify(r)
    r.val = 'Changed'
end
modify(myrec)
print myrec.val

Output:

Original
Changed

Note that records are always passed by reference, even when specifically passing in an owned reference as argument. In the example below, the created record exists only for the duration of the function call. The function's local variable rec is initialized with a non-owned reference to the record. This non-owned reference is returned, and thus an invalid reference will be assigned to a. Trying to access a after this would return in a NullError exception.

def do_init(rec)
    rec.val = 'inited'
    return rec
end
# The following should be avoided:
a = do_init(Record())  # returns null ref!
It is advisable to not use Record() in arguments. Only use it to assign an owned reference to a local variable, or when returning a copy of a record.

Defining into a record

The def statement accepts identifier lookups within the function name. For example, one could define the function func5 as a member of myrec.

def myrec.func5(a, b)
    return a + b
end

In fact, def behaves like an assignment operator. The above code means:

  1. Look up myrec.
  2. Create a variable called func5 within myrec.
  3. Create a function object taking arguments (a, b) and assign it as the value of the variable myrec.func5.

Since functions are actually variables that reference function objects, function definitions can be made within the scope of a function.

def func6()
    def func7(): return 'local function'
end

func7 is not visible outside func6, just like any other local variable. However, one could return func7 out of func6 and then it could be used just like a regular top-level function.

Functions defined inside another function do not have visibility to variables in the outer function. Instead, each function has its own local namespace and may access the module's global namespace.

a = 'global scope'
def outer()
    a = 100
    print 'outer: a =', a
    def inner()
        print 'inner: a =', a
    end
    inner()
end
outer()

Output:

outer: a = 100
inner: a = global scope

Function variables

Since functions are just variables referencing function objects, one can trivially make an alias for a function with assignment. Unlike records, function objects are reference-counted, so a function remains available as long as there is at least one variable pointing to it.

$ def someFunc(): return 'works'

$ other = someFunc

$ print someFunc(), other()
works works

Functions can be passed as arguments.

def doCallback(a, b, cb)
    return cb(a, b)
end
doCallback(10, 15, workFunction)
Records 
 Scopes
script/walkthrough/functions.txt · Last modified: 2019-11-25 08:41 by skyjake