How can I do a Do While loop

Question

Many languages have a Do While loop, how can I do one in Mathematica ?

@J.M. Mr. Wizard deleted it... http://mathematica.stackexchange.com/q/44224/5478 — Kuba, Nov 14 '15 at 13:15
@Kuba, hmm, I'd vote to undelete if my powers weren't unilateral. Why not cast an undelete vote, and hope others do so as well? (That will have the unfortunate effect of making this a dupe, tho.) — J. M.'s missing motivation, Nov 14 '15 at 13:24
Alright I set this one as a dupe. If anyone thinks the other thread should be reopened, cast your vote. — J. M.'s missing motivation, Nov 14 '15 at 13:29

LLlAMnYP · Answer 1 · 2015-11-14T12:59:02.870

5

This can be done much easier by putting the body of the loop into the test, like so:

While[body;test]

For example:

While[False,Print["Evaluated body"]]

gives no output, whereas

While[Print["Evaluated body"];False]
(* Evaluated body *)

does.

PS: The documentation for While presents my approach as the first example under "Scope" and @faysou's approach under "Generalizations and extensions".

edited Nov 14 '15 at 12:59

answered Nov 14 '15 at 12:54

LLlAMnYP

11,486
26
65

Nice, I didn't know this approach. I wrote another function as it makes it easier for me to explicitely see a DoWhile as an abstraction of a concept, plus I think it's a neat and simple illustration of metaprogramming. – faysou Nov 14 '15 at 13:10

score 3 · Accepted Answer · answered Nov 14 '15 at 12:44

Using some basic meta programming it's possible to do it.

SetAttributes[DoWhile,HoldAll];
DoWhile[expr_,condition_]:=
    While[True,
        expr;

        If[! condition,
            Break[];
        ];
    ];

For example

i=0
DoWhile[i++,i<0] (*i=1*)

i=-2
DoWhile[i++,i<0] (*i=0*)

How can I do a Do While loop

2 Answers2

Linked