visit_predicate.md

weight	3
title	visit(callback, predicate)

Iterates cells in row-major order and calls callback({ row, col, value }) for each cell where predicate({ row, col, value }) returns true. Reading and mutating the grid inside the callback is allowed.

Example

(move mouse to highlight 🐸 filled cells in the hovered col, and click to randomize q)
{{< p5-global-iframe quadrille="true" width="425" height="425" >}} 'use strict'; Quadrille.cellLength = 50; let q, hint;

function setup() { createCanvas(8 * Quadrille.cellLength, 8 * Quadrille.cellLength); q = createQuadrille(8, 8).rand(15, '🐸').rand(15, '🐯').rand(15, '🐮'); highlight(); }

function draw() { background('#D7BDE2'); drawQuadrille(q); drawQuadrille(hint); }

function mousePressed() { q.randomize(); highlight(); }

function mouseMoved() { highlight(); }

function highlight() { hint = createQuadrille(8, 8); q.visit( ({ row, col }) => hint.fill(row, col, color(0, 140)), ({ value, col }) => value === '🐸' && col === q.mouseCol ); } {{< /p5-global-iframe >}}

{{% details title="code" open=true %}}

Quadrille.cellLength = 50;
let q, hint;

function setup() {
  createCanvas(8 * Quadrille.cellLength, 8 * Quadrille.cellLength);
  q = createQuadrille(8, 8).rand(15, '🐸').rand(15, '🐯').rand(15, '🐮');
  highlight();
}

function draw() {
  background('#D7BDE2');
  drawQuadrille(q);
  drawQuadrille(hint);
}

function mousePressed() {
  q.randomize();
  highlight();
}

function mouseMoved() {
  highlight();
}

function highlight() {
  hint = createQuadrille(8, 8);
  q.visit(
    ({ row, col }) => hint.fill(row, col, color(0, 140)),
    ({ value, col }) => value === '🐸' && col === q.mouseCol
  );
}

{{% /details %}}

{{< callout type="info" >}}

• The predicate decides which cells are visited (e.g., only 🐸 in the current column).
• The callback defines what to do with those visited cells (e.g., fill them with semi-transparent color). {{< /callout >}}

Syntax

visit(callback, predicate)

Parameters

Param	Description
callback	Function called for each visited cell, receiving an object { row, col, value }. Its return value is ignored
predicate	A function ({ row, col, value }) => boolean. Only cells for which the predicate returns true are visited