Question

Is there any difference in meaning between t<'a> and 'a t in F#? Can they be used interchangeably even after declaration?

Answer 1

There is no difference, and yes, they can be used interchangeably even after declaration.

But do note the F# Component Design Guidelines recommendation (Section 4.2):

Consider using the prefix syntax for generics (Foo<T>) in preference
to postfix syntax (T Foo), with four notable exceptions (list,
option, array, ref).

F# inherits both the postfix ML style of naming
generic types, e.g. “int list” as well as the prefix .NET style, e.g.
“list<int>”. You should prefer the .NET style, except for four
specific types. For F# lists, use the postfix form: “int list”
rather than “list<int>”. For options, use the postfix form: “int option”
rather than “option<int>”. For arrays, use the syntactic name
“int[]” rather than either “int array” or “array<int>”. For refs,
use “int ref” rather than “ref<int>” or “Ref<int>”. For all other
types, use the prefix form: “HashSet<int>”, “Dictionary<string,int>”,
since this conforms to .NET standards

Also, you’ll get a compiler warning if you use the ML-style generic parameter list notation, e.g. ('a,'b) t vs. t<'a,'b>.

And while we’re at it, note the following recommendation in Section 3.1 of the same guide:

Do use PascalCase for generic parameter names in public APIs,
including for F#-facing libraries. In particular, use names like T, U,
T1, T2 for arbitrary generic parameters, and when specific names make
sense, then for F#-facing libraries use names like Key, Value, Arg
(but not e.g. TKey).

(though personally I tend to ignore this recommendation for F#-facing public libraries).