But why put it as a global metaswitcher instead of having different type infered from initial assignation qualifier?

Example:

    let integer answer be 42 — this is a constant
    set integer temperature be 37.2 — this is a mutable

Or with the more esoglyphomaniac fashion

    cst ↦ 123 // a constant is just a trivial map
    st ← 29.5 // initial assignment inferring float