RP42

RP42 is an advanced calculator with a visible stack of type-aware cards, units that compose, and colors and matrices as first-class citizens. 290+ built-in functions — from finance and statistics to timecode, color spaces, and linear algebra — sit one tap away. Under the hood it's pure RPN: the discipline as old as the HP-35 and still the fastest way to compute. The surface is modern SwiftUI. THE STACK, MADE VISIBLE Every value on the stack is a card, and what's on the card depends on what's in your hand. Numbers render in real LaTeX for publication-quality look. Booleans get a colored pill. Integers wear a radix badge. Colors show their swatch. Vectors and matrices lay out in grids. Quantities carry their unit. Timecode keeps its frames. Tap any card for a typed detail sheet: chromaticity diagrams, matrix grids, property breakdowns. CARD CALCS — WHOLE PROBLEMS, ONE CARD Swipe past the keypad and word categories to reach a grid of tiles for common problems. Tap TVM for time-value-of-money. RunPace for the pace-time-distance triangle. RunPlan for Daniels VDOT race predictions. Pizza Dough for a hydration-and-yeast recipe. Each opens a card of named rows you fill by tapping — pick which variable to solve for, edit any input, watch the rest recompute. Quantity rows carry per-row unit chips. Times read as clock. RunPlan's tables let you tap a predicted race time to lift it onto the stack. EQUATIONS ON THE STACK Push an equation the way you'd push a number. QUAD-EQ gives you ax² + bx + c = 0, rendered in publication-quality LaTeX. Tap it and a live solver opens: pick which variable to solve for, type the other values, and the answer updates as you scrub — no separate "compute" step. Twelve canned formulas ship built in — Ohm's law, kinematics, Pythagoras, circle area, sphere volume, wave phase velocity, kinetic energy — plus ->EXPR to lift your own from a string. UNITS THAT JUST WORK Tap a value, pick a unit. RP42 carries dimensional analysis through every operation: add 0.45_m to 12_in and you get a Quantity, not a stale double. CONVERT goes between any two compatible units. SIMPLIFY normalizes. UNIT-DEF lets you name your own. All eight SI dimensions, all the time. COLOR AND LINEAR ALGEBRA, FIRST-CLASS Push an RGB value and convert to XYZ, Lab, ICtCp, or YCbCr. EOTF and color space ride along as proper stack types. 20+ RGB working spaces — every SMPTE and camera-log space you'd want, plus ACES. Matrices are first-class: 3×3 multiply, dot, cross, Cramer's rule for systems of three. The chromaticity diagram and the matrix detail sheet live one tap away. AND 290+ FUNCTIONS ALL TOLD REPL plus slab keypad. Tooltips on every word with stack effects and a one-liner. Finance: HP-style TVM with P/Y, C/Y, and continuous compounding; cashflows, NPV/IRR; 38 financial functions. Statistics: mean, median, regression, percentiles. Timecode: SMPTE drop and non-drop; 24, 23.976, 29.97, 30 fps. Fractions: exact arithmetic on rationals. Geometry: circles, triangles, distance, area. FOUR THEMES Midnight, Obsidian, Dusk, Arctic. Pick one in Settings; the choice persists. BUILT ON RPN-LANG RP42 is built on rpn-lang, an open-source RPN engine. The dictionary is real Forth-style: words combine, definitions stack, and you can teach it new ones. The Swift layer is purely UI; the math is C++. The engine is yours to read, fork, or embed. New to RPN? You'll be fluent in five minutes. Already fluent? You're home.