“to do or not to do, is now the question”
In REBOL, contrary to Lisps, blocks or lists don’t evaluate by default. For better or for worse, this little difference is what makes REBOL - REBOL.
Fire up random online Lisp REPL and enter:
; Lisp
(print (+ 11 22))
; prints: 33 -- evaluated the list and printed the result
(print '(+ 11 22))
; prints: (+ 11 22) -- we had to quote it so it doesn't evaluate the list
When we give Lisp a block it evaluates it and prints the result. If we want to print the block we need to quote it. Lisp evaluates by default.
Rye came out of REBOL’s ideas and this is one of the core ones. So Rye and REBOL work the same here. What happens if we do the same in Rye shell …
; Rye
print { _+ 11 22 }
; prints: { _+ 11 22 } -- prints the block, doesn't evaluate
print do { _+ 11 22 }
; prints: 33 -- we had to *do* it, to evaluate it
Just the contrary than in lisp. If we give print function a block, it doesn’t evaluate it but prints it, and if we want to evaluate it, we have to do it. Rye doesn’t evaluate by default.
Rye has a function do that accepts one argument. This is usually a block of code, whict it evaluates (does) and returns the last value.
do { print "hello" 204 + 1030 }
; prints: hello
; returns: 1234
Bonus material
Blocks of code are just like other Rye blocks. As we said, function do evaluates the code in the block and returns the last value.
who-are-u: { print "James" "Bond" }
print first who-are-u
; prints: print
print do print who-are-u
; prints 3 lines:
; { print "James" "Bond" }
; James
; Bond
Evverything in Rye returns something, print returns the value it received.