dozen · RPN financial calculator library & desktop app

Two things in one repo:

• engine — a generic RPN calculator library: stack, registers, TVM, cash flows, statistics, depreciation, date math. No GUI dependency.
• App — a cross-platform financial calculator built with Wails v3 on top of the engine. macOS, Windows, Linux, iOS, Android.

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Library

go get github.com/shanehull/dozen/engine

Two layers: pure functions for direct math, and Engine for stack/keystroke behaviour that the app is built on.

Functional API

Rates are per-period fractions (0.05 = 5%). Inflows positive, outflows negative. engine.End (ordinary annuity) or engine.Begin (annuity due).

import "github.com/shanehull/dozen/engine"

pmt := engine.PMT(0.06/12, 360, 300000, 0, engine.End)
fmt.Printf("%.2f\n", -pmt) // 1798.65

npv := engine.NPV(0.10, -100000, 30000, 40000, 50000, 60000)
fmt.Printf("%.2f\n", npv)  // 38877.13

irr, _ := engine.IRR(-100000, 40000, 50000, 30000)
fmt.Printf("%.2f%%\n", irr*100) // 24.89%

TVM

FV(rate, n, pv, pmt float64, when Timing) float64
PV(rate, n, pmt, fv float64, when Timing) float64
PMT(rate, n, pv, fv float64, when Timing) float64
NPer(rate, pmt, pv, fv float64, when Timing) (float64, error)
Rate(n, pmt, pv, fv float64, when Timing) (float64, error)
SolveTVM(n, i, pv, pmt, fv float64, when Timing) (float64, error)

SolveTVM is the unified solver — pass math.NaN() for exactly one variable.

i, _ := engine.SolveTVM(360, math.NaN(), 300000, -1798.65, 0, engine.End)
fmt.Printf("%.4f%%\n", i*12*100) // 6.00% APR

Cash flows

NPV(rate float64, cashflows ...float64) float64
IRR(cashflows ...float64) (float64, error)

Depreciation

factorPct = declining-balance factor as percent (200 = double-declining).

DepSL(cost, salvage, life, period float64) (dep, remaining float64)
DepSOYD(cost, salvage, life, period float64) (dep, remaining float64)
DepDB(cost, salvage, life, period, factorPct float64) (dep, remaining float64)

Engine

Engine is an RPN calculator with a four-level stack, 20 memory registers, TVM and cash-flow slots, statistics accumulation, and program memory.

c := engine.New()

c.X = 2; c.Enter(); c.X = 3
c.Add()                    // c.X == 5

c.X = 360; c.SetN()        // FinN = 360
c.X = 5; c.SetI()          // FinI = 5
c.X = -1000; c.SetPV()     // FinPV = -1000
c.SolvePMT()               // c.X == monthly payment

c.X = 4; c.Sqrt()          // c.X == 2
c.X = 180; c.Sin()         // sine of 180 degrees

c.Snapshot()               // EngineState for persistence
c.Restore(state)

Methods

Category	Methods
Stack	Enter, Clx, Chs, XY, RollDown, RollUp, LastXRecall
Arithmetic	Add, Sub, Mul, Div, YPowX
TVM store	SetN, SetI, SetPV, SetPMT, SetFV
TVM solve	SolveN, SolveI, SolvePV, SolvePMT, SolveFV
Cash flow	NPV, IRR
Amortization	Amortize
Bonds	BondPrice, BondYield
Depreciation	DepreciationSL, DepreciationSOYD, DepreciationDB
Statistics	StatAdd, MeanX, MeanY, SDev, WeightedMean, LinEst, ClearStats
Scientific	Sin, Cos, Tan, Asin, Acos, Atan, Ln, Log, Sqrt, Sqr, Recip, Pi, Fact
Trig helpers	ToRad, ToDeg, ToRect, ToPolar, ToHMS, ToH
Percent	Pct, PctChg, PctTotal
Utility	Abs, Intg, Frac, Exp, Exp10
Date	DaysBetween, DateAdd
Memory	Store(n), Recall(n)
Program	SST, BST, Goto(line)
State	Snapshot, Restore
Clear	ClearFin, ClearReg, ClearStats, ClearPgm

Fields

c.X, c.Y, c.Z, c.T                // stack registers
c.LastX                            // last X before operation
c.Mem[0]..c.Mem[19]                // 20 general registers
c.FinN, c.FinI, c.FinPV, c.FinPMT, c.FinFV  // TVM registers
c.FinCF0, c.FinCFj, c.FinNj, c.FinCfCnt     // cash-flow registers
c.AmortN, c.AmortInt, c.AmortPrin           // amortization results
c.Flags.Begin, c.Flags.Dmy, c.Flags.Angle   // calculator mode
c.Flags.StackLift                             // stack lift flag
c.Program, c.PgmLen, c.PgmPC                 // program storage

Examples

go run examples/mortgage/main.go    # $300K mortgage payment
go run examples/solve-tvm/main.go   # unified TVM solver
go run examples/npv/main.go         # NPV + IRR
go run examples/fv/main.go          # future value
go run examples/stats/main.go       # statistics (engine)
go run examples/date/main.go        # date calculations (engine)

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App

A financial RPN calculator: stack, memory, TVM, cash flows, statistics, programs. Built with Wails v3.

wails3 dev

Keyboard

Key	Action
0–9, .	digits
+ - * /	+ − × ÷
Enter	ENTER
Esc / Backspace	CLx
%	%
f / g	arm gold / blue shift
n i p m v	n i PV PMT FV
s	STO prefix
r	RCL prefix
x	x↔y

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Development

go test ./engine/           # unit + regression tests
go test -run TestUI .       # UI integration tests
go vet ./...                # lint
wails3 dev                  # app with hot reload

License

MIT