Mixed fraction input

Question

How do I make mathematica treat $5\frac{1}{2}$ as a mixed fraction rather than 5 times one-half?

I'm using typesetting keyboard shortcuts (if that's important)

Currently I'm using $(5 + \frac{1}{2})$ to achieve this.

Answer 1

You can add an input alias to do this. For example:

CurrentValue[EvaluationNotebook[], {InputAliases, "mf"}] = TemplateBox[
    {"\[SelectionPlaceholder]","\[Placeholder]","\[Placeholder]"},
    "MixedFraction",
    DisplayFunction->(RowBox[{#1, FractionBox[#2,#3]}]&),
    InterpretationFunction->(RowBox[{#1,"+", FractionBox[#2,#3]}]&)
];

Here is a short animation showing it in action:

Answer 2

\[ImplicitPlus] can be entered as ESC+ESC:

5\[ImplicitPlus](1/2)
(*  11/2  *)

It works for entering in the Front End, but it is automatically converted to Plus: