If it ends up being difficult to find a syntax for function definition that feels right and fits within the existing Soulver syntax, another option could be to separate function from data. It could work in a few ways:

* Let the user define functions in Soulver's settings alongside Global Variables that they can use. When sharing a sheet with others, include any globally defined functions that the sheet depends on. When another user imports the sheet, prompt them to add these required functions to their global custom function library. On a conflicting name, ask for a new name and update any references to the function in the sheet.

* Instead of defining functions globally, let the user define them as part of the metadata of a sheet.

If you mean x and y to be expressions, this would be great. But our example is just two numbers, and the min of two numbers is immediately obvious (at least it seems to to me), so it wouldn't be useful if x and y are just numbers.

Supporting region-specific delimiters in function input seems to be a costly straightjacket. When calling a function, you could require a period for decimal and no thousands delimitters in bare numbers. That would also allow support for soulver's multi-word variables. I think many users would appreciate the extra structure of brackets and comma delimitters.

min(1000.32, foo)

min(my dog, my cat)

Regarding syntax, I had thought that something C/R like would be comfortable for the biggest set of users, e.g.

min = function(x, y){ if (x < y) then x else y}

But seeing the approach of treating all formulas as function bodies discussed below, that looks preferable. So elegant to define a variable, then use that definition as a function simply by appending () to the variable name!…

min = if x < y then x else y

min(3, 4 ) // outputs 3

min(x=3, y=4) // outputs 3

(still prefer the comma delimiter - reduced the mental work load of groking the input string

Something to consider; for functions to be really useful, having a concept of “global” across sheets would be really beneficial, similar to this feature request:

That way we could create a sheet of functions we use and add to it over time.

I would also love to see user-defined functions implemented, however my vote would go with the more standard parenthesised syntax, so:

min(x, y) = if x < y then x else y

Used:

min(0, 1)

This is also more consistent with Soulver's built-in functions.

Interesting idea!