How to write this in idiomatic F#?

gistfile1.txt

let isValid input = 
    input 
    |> parse
    /*smelly and doesn't scale, what's the F# way of combining predicates?*/
    |> (fun p -> predicate1 p && predicate2 p) 

You can easily write helper functions:

/// Combine two predicates
let addPred predicate1 predicate2 = 
    fun p -> predicate1 p && predicate2 p

/// Combine a list of predicates
let combinePred aListOfPred = 
    aListOfPred |> List.reduce addPred

so your code becomes:

// some predicates
let isEven x = (x%2 = 0)
let isFizz x = (x%3 = 0)
let isBuzz x = (x%5 = 0)

// a validation function
let isValid input = 
    input 
    |> addPred isEven isFizz

// test
[1..30] |> List.filter isValid

let isValid2 input = 
    let megaPred = combinePred [isEven;isFizz;isBuzz]
    input 
    |> megaPred 

// test
[1..30] |> List.filter isValid2

If you are doing input validation though, I suggest you try avoid booleans if you can, and think about transformation oriented approaches. That is, taking an input and transforming it to either a success (with associated data), or a a failure (with associated error messages). I have a talk about this approach that might be useful: http://fsharpforfunandprofit.com/rop/

Cheers!

Ahh, I love the smell of idiomatic F# in the morning!
Thanks for the pointers!

I've watched your ROP talk before but thought it'd be a tad too much to just solve the adventofcode problems. Just give me a few more weeks with F# and I'll get there :)