Are there programming languages in which 2½ is read as a numeric rational literal?
I feel like if any language would get this, Racket would. (Spoiler: Racket doesn't.)
@technomancy perl6 will parse ½ as 0.5, but rejects 2½. 2 + ½ does work
@technomancy well, it renders back out as 0.5, but it appears to be a "Rat"
@rx So close!

@technomancy also i seem to recall the factor language parsing 2+1/2 as the rational 5/2. no unicode, but true mixed fraction literals nonetheless

(note: 2+1/2 is treated as a single token; factor is stack-based so doing a runtime addition would look like 2 1/2 +)

@technomancy you could try the Wolfram Language (Mathematica). That language never ceases to amaze me with the things it simply accepts as input or function arguments.
@technomancy I should check if Purescript gets it. A ton of Unicode stuff works there.
@technomancy Maybe one of the scientific computing languages?