Question

I want to compare user input from READ with a string, like so:

CL-USER 36 > (equalp (read) "same")
same
NIL

However, as you can see, even though I type in “same,” EQUALP says my input and the string are different. How can I compare these two?

Answer 1

You can use read-line for this:

CL-USER> (equalp (read-line) "same")
same
T

read would return a symbol:

CL-USER> (type-of (read))
same
SYMBOL

From the Hyperspec:

read parses the printed representation of an object from input-stream
and builds such an object.

You just want to read a string, whereas read parses the input and constructs Lisp objects from it.

To get strings out of read, you’d have to use the “printed representation” of strings, i.e. put them in double quotes:

CL-USER> (equalp (read) "same")
"same"
T

(BTW: There is string= for string comparisons; equalp will ignore case.)