lisp 里的循环很多种

尤其是loop 千变万化，我也搞不懂，

找了一点示例代码放这里：

Iteration for each element in a list:

> (loop for i in '(1 2 3) do (print i))
1
2
3

Iteration for each cdr of a list:

> (loop for i on '(1 2 3) do (print i))
(1 2 3)
(2 3)
(3)

Iteration for each element in a vector:

> (loop for i across #(1 2 3) do (print i))
1
2
3

Iteration for each key of a hashtable:

> (setf h (make-hash-table))
> (setf (gethash 'a h) 1)
> (setf (gethash 'b h) 2)
> (loop for k being the hash-key of h do (print k))
b
a

Iteration for each value of a hashtable:

> (loop for v being the hash-value of h do (print v))
2
1

Iteration for each key-value pair of a hashtable:

> (loop for k being the hash-key using (hash-value v) of h do (format t "~a ~a~%" k v))
b 2
a 1

i=1, while i <= 3:

> (loop for i from 1 to 3 do (print i))
1
2
3

i=1, while i <= 3: (different step)

> (loop for i from 1.0 to 3.0 by 0.5 do (print i))
1.0
1.5 
2.0 
2.5 
3.0

i=3, while i >= 1:

> (loop for i from 3 downto 1 do (print i))
3
2
1

i=3, while i >= 1: (different step)

> (loop for i from 3.0 downto 1.0 by 0.5 do (print i))
3.0 
2.5 
2.0 
1.5 
1.0

i=1, while i < 3:

> (loop for i from 1 below 3 do (print i))
1
2

i=3, while i > 1:

> (loop for i from 3 above 1 do (print i))
3
2

Adding initialization:

> (loop with a = '(1 2 3) for i in a do (print i))
1
2
3

Adding subordinate variables:

> (loop for i from 1 to 3 for x = (* i i) do (print x))
1
4
9

Adding conditional branch for each element:

> (loop for i from 1 to 3 when (oddp i) do (print i))
1
3

Adding a termination condition (while):

> (loop for i from 1 to 3 while (< i 2) do (print i))
1

Adding a termination condition (until):

> (loop for i from 1 to 3 until (< 2 i) do (print i))
1
2

Collecting results as an element of a list:

> (loop for i from 1 to 3 collect (* i i))
(1 4 9)

Concatenating results as a list:

> (loop for i from 1 to 3 append (list i i))
(1 1 2 2 3 3)

Counting:

> (loop for i from 1 to 3 count (oddp i))
2

Summation:

> (loop for i from 1 to 3 sum (* i i))
14

Taking the maximum value:

> (loop for i from 1 to 3 maximize (mod i 3))
2

Taking the minimum value:

> (loop for i from 1 to 3 minimize (mod i 3))
0

CL-USER> (loop for x below 10
collect (loop for y below 10
collect (+ x y)))
((0 1 2 3 4 5 6 7 8 9) (1 2 3 4 5 6 7 8 9 10) (2 3 4 5 6 7 8 9 10 11)
(3 4 5 6 7 8 9 10 11 12) (4 5 6 7 8 9 10 11 12 13) (5 6 7 8 9 10 11 12 13 14)
(6 7 8 9 10 11 12 13 14 15) (7 8 9 10 11 12 13 14 15 16)
(8 9 10 11 12 13 14 15 16 17) (9 10 11 12 13 14 15 16 17 18))
CL-USER> (loop for x below 10
for y below 10
collect (+ x y))
(0 2 4 6 8 10 12 14 16 18)
CL-USER> (loop for i
from 0
do (print i)
when (= i 5)
return 'falafel)

0
1
2
3
4
5
FALAFEL
CL-USER>

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lisp 里的循环loop macro

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