September 2017 Update

Task/Call-a-function/Ol/call-a-function.ol

@@ -0,0 +1,119 @@
+; note: sign "==>" indicates expected output
+
+;;; Calling a function that requires no arguments
+(define (no-args-function)
+   (print "ok."))
+)
+
+(no-args-function)
+; ==> ok.
+
+
+;;; Calling a function with a fixed number of arguments
+(define (two-args-function a b)
+   (print "a: " a)
+   (print "b: " b))
+)
+
+(two-args-function 8 13)
+; ==> a: 8
+; ==> b: 13
+
+
+;;; Calling a function with optional arguments
+(define (optional-args-function a . args)
+   (print "a: " a)
+   (if (null? args)
+      (print "no optional arguments"))
+   (if (less? 0 (length args))
+      (print "b: " (car args)))
+   (if (less? 1 (length args))
+      (print "c: " (cadr args)))
+   ; etc.
+)
+
+(optional-args-function 3)
+; ==> a: 3
+; ==> no optional arguments
+(optional-args-function 3 8)
+; ==> a: 3
+; ==> b: 8
+(optional-args-function 3 8 13)
+; ==> a: 3
+; ==> b: 8
+; ==> c: 13
+(optional-args-function 3 8 13 77)
+; ==> a: 3
+; ==> b: 8
+; ==> c: 13
+
+
+;;; Calling a function with a variable number of arguments
+; /same as optional arguments
+
+
+;;; Calling a function with named arguments
+; /no named arguments "from the box" provided, but it can be simulated using builtin maps (named "ff")
+(define (named-args-function args)
+   (print "a: " (get args 'a 8))
+   (print "b: " (get args 'b 13))
+)
+
+(named-args-function #empty)
+; ==> a: 8
+; ==> b: 13
+(named-args-function (list->ff '((a . 3))))
+; ==> a: 3
+; ==> b: 13
+(named-args-function (list->ff '((b . 7))))
+; ==> a: 8
+; ==> b: 7
+(named-args-function (list->ff '((a . 3) (b . 7))))
+; ==> a: 3
+; ==> b: 7
+
+
+;;; Using a function in first-class context within an expression
+(define (first-class-arg-function arg a b)
+   (print (arg a b))
+)
+
+(first-class-arg-function + 2 3)
+; ==> 5
+(first-class-arg-function - 2 3)
+; ==> -1
+
+
+;;; Obtaining the return value of a function
+(define (return-value-function)
+   (print "ok.")
+   123)
+
+(let ((result (return-value-function)))
+   (print result))
+; ==> ok.
+; ==> 123
+; actually
+
+
+;;; Is partial application possible and how
+(define (make-partial-function n)
+   (lambda (x y)
+      (print (n x y)))
+)
+
+(define plus (make-partial-function +))
+(plus 2 3)
+; ==> 5
+(define minus (make-partial-function -))
+(minus 2 3)
+; ==> -1
+
+
+; TBD:
+;;; Using a function in statement context
+;;; Using a function in first-class context within an expression
+;;; Obtaining the return value of a function
+;;; Distinguishing built-in functions and user-defined functions
+;;; Distinguishing subroutines and functions
+;;; Stating whether arguments are passed by value or by reference