On Sun, May 23, 2021 at 08:44:32PM -0500, polifemo wrote:
> `(let @ 1 (let @ 10 (let @ 20 (up 2 @))))`
This are two misunderstandings in this example:
1. It has not a good idea to bind '@' in a 'let' expression. '@' is set
implicitly by flow- and logic-functions, so a correct usage would be
(and 1 (or 10 (while 20 (up 2 @))))
or - more realistically -
(and (foo) (or (bar) (while (zup) (up 2 @))))
2. 'up' does not care about 'let', 'use', 'for' etc. They are ignored. An up
"enclosing environment" always means the enclosing *function* environment. So
all the above 'let's all run in the same environment. The same rule applies
to the environment offsets to 'eval' and 'run'.
> returns 1, as I expected, if I enclose the 'up expression inside a function
This return value of '1' just happens because the environment setup in bindeng
'@' in 'let' is undefined.
Let me try to give an example.
(when 7 # The result of 'when' is what we are interested in
(extract
'((N) # Here we are in a function
(when (num? N) # 'when' sets '@'
(+ N @) ) ) # so we add the wrong '@'
(1 a 2 b 3)))
-> (2 4 6)
(when 7
(extract
'((N) # in a function
(when (num? N)
(+ N (up 1 @)) ) ) # Here we get the '7'
(1 a 2 b 3)))
-> (8 9 10)
☺/ A!ex
--
UNSUBSCRIBE: mailto:[email protected]?subject=Unsubscribe
