feat(evaluator): Add P1 financial/date/type-check functions

[arcaputo3]

Background

These 14 functions enable complete financial modeling: TVM functions for debt schedules, date functions for projections, and type checking for validation.

Functions to Implement

Date Functions

Function	Signature	Use Case
EOMONTH	EOMONTH(start_date, months)	End of month N months away
EDATE	EDATE(start_date, months)	Same day N months away
YEARFRAC	YEARFRAC(start, end, [basis])	Fraction of year between dates

Time Value of Money (TVM)

Function	Signature	Use Case
PMT	PMT(rate, nper, pv, [fv], [type])	Loan payment
PV	PV(rate, nper, pmt, [fv], [type])	Present value
FV	FV(rate, nper, pmt, [pv], [type])	Future value
RATE	RATE(nper, pmt, pv, [fv], [type], [guess])	Interest rate
NPER	NPER(rate, pmt, pv, [fv], [type])	Number of periods

Statistics

Function	Signature	Use Case
MEDIAN	MEDIAN(number1, [number2], ...)	Median value
STDEV	STDEV(number1, [number2], ...)	Standard deviation (sample)
COUNTA	COUNTA(value1, [value2], ...)	Count non-empty cells

Type Checking

Function	Signature	Use Case
ISBLANK	ISBLANK(value)	Check if empty
ISNUMBER	ISNUMBER(value)	Check if numeric
ISTEXT	ISTEXT(value)	Check if text

Implementation Notes

TVM Functions

Standard financial formulas. type parameter: 0 = end of period (default), 1 = beginning.

YEARFRAC Basis

• 0 = US 30/360 (default)
• 1 = Actual/actual
• 2 = Actual/360
• 3 = Actual/365
• 4 = European 30/360

RATE

Requires Newton-Raphson iteration (similar to IRR/XIRR).

Acceptance Criteria

• All 14 functions parse correctly
• All 14 functions evaluate correctly
• Tests for TVM functions against Excel
• Tests for date functions with edge cases
• Update FunctionParser.buildRegistry()

Priority

P1 - High value for financial modeling

Labels

enhancement, evaluator

[arcaputo3]

Cross-Reference Update

This issue has been expanded into more granular issues for better tracking:

Statistics & Counting (from this issue)

• feat(evaluator): Add COUNTA, COUNTBLANK #118 - COUNTA, COUNTBLANK
• feat(evaluator): Add MEDIAN, STDEV, VAR (statistics) #123 - MEDIAN, STDEV, VAR (statistics)

Type Check Functions (from this issue)

• Planned for v0.6.0, will be part of function expansion

Financial Functions

Note: EOMONTH, EDATE, YEARFRAC already implemented in v0.5.0

See the full roadmap at #109 (v0.5.1) through #137 (v0.8.0+) for comprehensive feature planning.

[arcaputo3]

Closing — all P1 functions are implemented: PMT, FV, PV, RATE, NPER, NPV, IRR, XIRR, XNPV, EOMONTH, EDATE, YEARFRAC, ISNUMBER, ISTEXT, ISBLANK. Only TYPE is missing — not worth keeping this umbrella open for one function.