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(*
A library implementing a very simple string interpolation facility.
An example of usage is
print(format "The square of $ is $\n" ["3", "9"])
*)
signature FORMAT = sig
val format : string -> string list -> string
end
structure Format = struct
exception ArityError of string
fun checkArity(templN1, argsN) = let
val n1 = Int.toString (length templN1 - 1)
val n = Int.toString (length argsN)
in
if n1=n then () else raise ArityError("Expected "^n1^" arguments, got"^n)
end
val rec interp' =
fn ([t], [], acc) => concat(rev (t :: acc))
| (t :: templ, a :: args, acc) => interp'(templ, args, t :: a :: acc)
| _ => raise ArityError "This should never happen"
and interp'' =
fn (templN1, argsN) => (
checkArity (templN1, argsN); interp' (templN1, argsN, []))
and format =
fn templ => let
val templN1 = String.fields (fn c => c = #"$") templ
in
fn args => interp'' (templN1, args)
end
end: FORMAT
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