[lispm]

The numeric tower in Common Lisp may surprise us with simple things as addition:

  (+ #c(10 -1) #c(20 1))

the result of adding these two complex numbers is the integer 30.

[Paul-Craft]

Huh. I did not know that. I am surprised that it actually coerces the result to an integer, although that's certainly an artificial type edge case.

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    * (+ #c(10 -1) #c(20 1))
    30
    * (type-of (+ #c(10 -1) #c(20 1)))
    (INTEGER 0 4611686018427387903)

For example, if you do this, you do get a complex number.

    * (type-of (+ #c(10 -1) #c(20 1.0))) 
    (COMPLEX (SINGLE-FLOAT 0.0 30.0))