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42minjoy.in2
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42minjoy.in2
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(* vi: filetype=joy
*)
(* RECURSIVE FUNCTIONS, non-recursive computation *)
(* "last" is a tail-recursive function *)
[ Smith Jones Robinson ] last .
(* now let us look at the (recursive) definition of "last" *)
[last] definition .
[ Smith Jones Robinson ] [last] definition i .
(* using the x-combinator *)
[Smith Jones Robinson]
[ swap dup rest null
[ car swap pop ]
[ cdr swap x ] (* NOTE x-combinator *)
branch ]
x . (* REPEAT x-combinator *)
(* using the y-combinator *)
[Smith Jones Robinson]
[ swap dup rest null
[ car swap pop ]
[ cdr swap i ] (* NOTE i-combinator *)
branch ]
y . (* NOTE y-combinator *)
(* "factorial" is not tail-recursive *)
6 factorial_rec .
(* using the x-combinator *)
6
[ swap dup 1 <=
[ pop pop 1 ]
[ dup pred rolldown x * ]
branch ]
x .
(* using the y-combinator *)
6
[ swap dup 1 <=
[ pop pop 1 ]
[ dup pred rolldown i * ]
branch ]
y .
(* "QUICKSORT" *)
[1 9 2 8 3 7 4 6 5] quicksort .
[5 6 4 7 3 8 2 9 1] quicksort .
[1 2 3 4 5 6 7 8 9] quicksort .
[9 8 7 6 5 4 3 2 1] quicksort .
(* now look at the definition of quicksort: *)
[quicksort] definition .
(* sorting lists on first item *)
[ [1 Smith] [3 Jones] [2 Robinson] [4 Brown] ]
quicksort1 .
(* sorting on symbol *)
[] (* initial class-list in COMPUTATIONAL CHRONOSCOPY *)
[NURKS Peter 1989 year 3 major Computer Science] cnos
[ABELSON Mary 1990 year 2 major Logic] cnos
[ZEEMAN Fred 1988 year 2 major Accounting] cnos
[MORRIS Janna 1992 year 1 major undecided] cnos
(* now sort on surname and print *)
quicksort1 dup [putln] step pop .