theEnvironment

theEnvironment( 
[ u_funobj ] 
) 
=> e_environment / nil 

Description

(SKILL++ mode only) Returns the top level environment if called from a SKILL++ top-level. Returns the enclosing lexical environment if called within a SKILL++ function. Returns the associated environment if passed a SKILL++ function object. Otherwise returns nil.

• In SKILL++, there is a unique top-level environment that implicitly encloses all other local environments. If you do not pass the optional argument, when you call theEnvironment from a SKILL++ top-level, theEnvironment returns this environment. The schemeTopLevelEnv function also returns this environment.
• If you call theEnvironment from within a SKILL++ function and if you do not pass the optional argument, theEnvironment returns the enclosing lexical environment.
• If you are in debug mode, you can pass a closure to theEnvironment. A closure is another term for a function object returned by evaluating a SKILL++ lambda expression which abstractly, consists of two parts:
  • The code for the lambda expression.
  • The environment in which the free variables in the body are bound when the lambda expression is evaluated.
• If you call theEnvironment from a SKILL function and do not pass a closure, then theEnvironment function returns nil.

Arguments

u_funobj

Optional argument. Should be a SKILL++ closure.

Value Returned

nil	Returned when called from a SKILL function and you do not pass a SKILL++ closure as the optional argument.
e_environment	Either the top-level environment, or the enclosing environment, or the closure’s environment.

Examples

Returns the environment that the let expression establishes. The value of Z is an environment in which x is bound to 3. Each time you execute the above expression, it returns a different environment object, as you can tell by observing the print representation.

Z = let( ( x ) 
    x = 3 
    theEnvironment() 
    ) ; let
=> envobj:0x1e0060

Uses theEnvironment to illustrate that the variable initialization expressions in a let expression refer to the enclosing environment.

Z = let( (( x theEnvironment()))
    x
    )
=> envobj:0x2fc018
eq( schemeTopLevelEnv() Z ) => t 

Uses theEnvironment to illustrate that the variable initialization expressions in a letrec expression refers to the letrec’s environment.

V = letrec( (( x theEnvironment()))
    x
    )
=> envobj:0x33506c
eq( schemeTopLevelEnv() V ) => nil
eq( V~>x V ) => t

Returns the environment that the nested let expressions establish. Notice that assigning it to the top-level variable W makes it persistent.

W = let( (( r 3 ) ( y 4 ))
        let( (( z 5 ) ( v 6 ))
            theEnvironment()
            ) ; let
        ) ; let
=> envobj:0x456030c
W~>r => 3
W~>z => 5
W~>?? => ((z(5) (v 6)) ((r 3) y(4)))

Returns a function object which, in turn, returns its local environment.

Q = letrec( 
    ( ;; begin locals
        ( X 6 )
        ( self 
            lambda( ( ) 
                theEnvironment() 
                ) ; lambda
            ) ; self
        ) ;;; end of locals
    self 
    ) ; letrec 
=> funobj:0x1e38b8
Q() => envobj:0x1e00e4
theEnvironment( Q ) => envobj:0x1e00e4 ;in debug mode only

Related Topics

Core Functions

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