4 ms·

I see. So what is the output of Read macros? It has to be text, right, since only the compiler will be able to deal with tokens/objects?

Jtsummers 3y ago
Read macros are processed at read time, the result is a change to the way the `read` function operates. The output is a lisp object. On Lisp Ch 17, page 224: https://sep.turbifycdn.com/ty/cdn/paulgraham/onlisp.pdf https://sep.turbifycdn.com/ty/cdn/paulgraham/onlisp.pdf CLTL2 Section 22.1.1: https://www.cs.cmu.edu/Groups/AI/html/cltl/clm/node188.html#SECTION002611000000000000000 https://www.cs.cmu.edu/Groups/AI/html/cltl/clm/node188.html#... - Goes into a lot of detail on how the reader works. The macros most people mean when they talk about Lisp macros are discussed in CLTL2 Ch 8. They are expanded during evaluation or compilation. CLTL2 CH 8: https://www.cs.cmu.edu/Groups/AI/html/cltl/clm/node97.html https://www.cs.cmu.edu/Groups/AI/html/cltl/clm/node97.html Read macros are able to produce (or not produce) lisp objects by taking control of the stream processing for some period of time.
hayley-patton 3y ago
The compiler deals with code in S-expression form, represented as lists and atoms. Reader macros produce Common Lisp objects.
lispm 3y ago
reader macros create Lisp data. The compiler/interpreter gets as input Lisp data. Let's use READ, DESCRIBE and EVAL to see that working: CL-USER 17 > (defun example (&aux input result) (terpri) ; newline (write-string "Input> ") (finish-output) (terpri) (setf input (read)) ; reading from input stream (terpri) (describe input) ; what did we read? (terpri) (write-string "Output>") (setf result (eval input)) ; evaluation (terpri) (write-string "Result>") (print result) ; printing the result (values)) ; return nothing EXAMPLE CL-USER 18 > (example) Input> (progn (print (+ 1 3)) (print 'done)) (PROGN (PRINT (+ 1 3)) (PRINT (QUOTE DONE))) is a LIST 0 PROGN 1 (PRINT (+ 1 3)) 2 (PRINT (QUOTE DONE)) Output> 4 DONE Result> DONE As you can see READ in actual Lisp takes input from the keyboard and returns a list as data. EVAL is then taking code as a list and evaluates it to a value, as side effects there might be printed output of the program.

Jtsummers 3y ago

Read macros are processed at read time, the result is a change to the way the `read` function operates. The output is a lisp object. On Lisp Ch 17, page 224: https://sep.turbifycdn.com/ty/cdn/paulgraham/onlisp.pdf https://sep.turbifycdn.com/ty/cdn/paulgraham/onlisp.pdf CLTL2 Section 22.1.1: https://www.cs.cmu.edu/Groups/AI/html/cltl/clm/node188.html#SECTION002611000000000000000 https://www.cs.cmu.edu/Groups/AI/html/cltl/clm/node188.html#... - Goes into a lot of detail on how the reader works. The macros most people mean when they talk about Lisp macros are discussed in CLTL2 Ch 8. They are expanded during evaluation or compilation. CLTL2 CH 8: https://www.cs.cmu.edu/Groups/AI/html/cltl/clm/node97.html https://www.cs.cmu.edu/Groups/AI/html/cltl/clm/node97.html Read macros are able to produce (or not produce) lisp objects by taking control of the stream processing for some period of time.

hayley-patton 3y ago

The compiler deals with code in S-expression form, represented as lists and atoms. Reader macros produce Common Lisp objects.

lispm 3y ago

reader macros create Lisp data. The compiler/interpreter gets as input Lisp data. Let's use READ, DESCRIBE and EVAL to see that working: CL-USER 17 > (defun example (&aux input result) (terpri) ; newline (write-string "Input> ") (finish-output) (terpri) (setf input (read)) ; reading from input stream (terpri) (describe input) ; what did we read? (terpri) (write-string "Output>") (setf result (eval input)) ; evaluation (terpri) (write-string "Result>") (print result) ; printing the result (values)) ; return nothing EXAMPLE CL-USER 18 > (example) Input> (progn (print (+ 1 3)) (print 'done)) (PROGN (PRINT (+ 1 3)) (PRINT (QUOTE DONE))) is a LIST 0 PROGN 1 (PRINT (+ 1 3)) 2 (PRINT (QUOTE DONE)) Output> 4 DONE Result> DONE As you can see READ in actual Lisp takes input from the keyboard and returns a list as data. EVAL is then taking code as a list and evaluates it to a value, as side effects there might be printed output of the program.