Just another update

Task/Call-a-function/Forth/call-a-function.fth

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+a-function         \ requiring no arguments
+a-function         \ with a fixed number of arguents
+a-function         \ having optional arguments
+a-function         \ having a variable number of arguments
+a-function         \ having such named arguments as we have in Forth
+' a-function var ! \ using a function in a first-class context (here: storing it in a variable)
+a-function         \ in which we obtain a function's return value
+
+                   \ forth lacks 'statement contenxt'
+                   \ forth doesn't distinguish between built-in and user-defined functions
+                   \ forth doesn't distinguish between functions and subroutines
+                   \ forth doesn't care about by-value or by-reference
+
+\ partial application is achieved by creating functions and manipulating stacks
+: curried  0 a-function ;
+: only-want-third-argument 1 2 rot a-function ;
+
+\ Realistic example:
+: move ( delta-x delta-y -- )
+  y +!  x +! ;
+
+: down ( n -- )  0 swap move ;
+: up ( n -- )    negate down ;
+: right ( n -- ) 0 move ;
+: left ( n -- )  negate right ;