Template strings in F#?

Question

I'm new to F#, and want to know if there is anything in F# similar to template strings in Python. So I can simply do something like:

    >>> d = dict(who='tim', what='car')
    >>> Template('$who likes $what').substitute(d)
    'tim likes car'

Answer 1

The idiomatic way of doing that in F# is with sprintf:

let newString = sprintf "First Name: %s Last Name: %s" "John" "Doe"

Additionally, you have access to the .net String.Format:

let newString = String.Format("First Name: {0} Last Name: {1}", "John", "Doe")

The benefit of the first one is that it is type-safe (i.e. you can't pass a string to an integer formatter like "%d"). As noted by Benjol in the comments, it's not possible to pass a format string to sprintf because it is statically typed. See here for more information on that.

Answer 2

New in F# 5 is string interpolation:

let firstName = "John" 
let lastName = "Doe" 

let newString = $"First Name: {firstName} Last Name: {lastName}" 

Or without local bindings (note the triple quotes):

let newString = $"""First Name: {"John"} Last Name: {"Doe"}"""

Older versions of F# should use sprintf:

let newString = sprintf "First Name: %s Last Name: %s" "John" "Doe"