Implement ISOMITTED function

[Jython1415]

Overview

Implement the ISOMITTED function for the named-functions library.

Description

Checks whether a value in a LAMBDA function is missing (omitted) and returns TRUE or FALSE.

Value Proposition

• Critical for creating LAMBDAs with optional parameters
• Enables more flexible function signatures
• Allows default parameter behavior within custom functions
• Essential for advanced LAMBDA patterns

Priority

HIGH

Category

Advanced LAMBDA Support

Implementation Notes

• This is a meta-function for LAMBDA parameters
• In Excel, works specifically with LAMBDA optional parameters
• Google Sheets may have different approach to optional parameters
• May need to research Google Sheets LAMBDA limitations
• Could potentially use sentinel values or special markers
• Test thoroughly with nested LAMBDAs

Research Needed

• How does Google Sheets handle optional LAMBDA parameters?
• Is there a native equivalent or workaround?
• What sentinel value works best (NA, empty, special marker)?

Related

Part of Excel function implementation initiative (#51)

[Jython1415]

Viable Workaround Exists

TL;DR

Google Sheets does support optional parameters via empty argument detection. No ISOMITTED function needed - use pattern directly.

How It Works

✅ Google Sheets allows double commas:

=LAMBDA(a, b, c)(1, , 3)  // b receives ""

✅ Empty arguments receive empty string (""):

=LAMBDA(text, separator, IF(separator = "", ",", separator))(...)

✅ Pattern for optional parameters:

formula: |
  LET(
    sep, IF(separator = "", ",", separator),  // Default to comma
    result, SPLIT(text, sep),
    result
  )

Limitation

Cannot distinguish:

• (, ,) - truly omitted
• ("", "") - explicitly passed empty strings

Both produce "". Requires user discipline.

Recommendation

Document the pattern rather than implementing ISOMITTED function:

1. Add to project docs: "Optional Parameters Pattern"
2. Show examples in existing functions (1-2 trailing optional params)
3. Users can apply pattern directly in their formulas

Best Use Cases

• 1-2 trailing optional parameters
• Clear "use default" semantics
• Example: separator, precision, padding value

Pattern is sufficient - no dedicated function needed. Close as documented.

[Jython1415]

I think Claude has it wrong above. ISOMITTED would be useful in LAMBDA as a semantic replacement is ISBLANK, but that is about it. I'll have to come back to it later and clarify. Info online was probably not very useful here.