Evaluating Medley compatibility with Practical Common Lisp code: Chapter 22

[pamoroso]

Chapter 22. LOOP for Black Belts

This is the continuation of the work on issue #609. To evaluate the compatibility of Medley Common Lisp with ANSI Common Lisp I'm testing on Medley the code of Peter Seibel's book Practical Common Lisp.

Adapting the code of chapter 22 involved only adding a handful of missing definitions.

Issues

All the expressions seem to work as expected except for the following which yield the error Loop form tail (...) remained unprocessed:

(loop repeat 5 
      for x = 0 then y
      for y = 1 then (+ x y)
      collect y)

(loop repeat 5
      for y = 1 then (+ x y)
      for x = 0 then y
      collect y)

(loop repeat 5 
      for x = 0 then y
      and y = 1 then (+ x y)
      collect y)

A similar loop expression causes the same error in the code of chapter 19. Is this code ANSI compliant? Does it trigger undefined behavior? Is this a limitation of Medley's loop implementation?

Other than that the loop implementation works well and covers several common cases.

Code

This is the full code I evaluated at a XCL Exec:

(loop for i upto 10 collect i)

(loop for i from 0 downto -10 collect i)

(loop for i in (list 10 20 30 40) collect i)

(loop for i in (list 10 20 30 40) by #'cddr collect i)

(loop for x on (list 10 20 30) collect x)

(loop for x on (list 10 20 30 40) by #'cddr collect x)

(loop for x across "abcd" collect x)

(loop repeat 5 
      for x = 0 then y
      for y = 1 then (+ x y)
      collect y)

(loop repeat 5
      for y = 1 then (+ x y)
      for x = 0 then y
      collect y)

(loop repeat 5 
      for x = 0 then y
      and y = 1 then (+ x y)
      collect y)

(loop for (a b) in '((1 2) (3 4) (5 6))
            do (format t "a: ~a; b: ~a~%" a b))

(defvar list '(a b c d e))

(loop for cons on list
    do (format t "~a" (car cons))
    when (cdr cons) do (format t ", "))

(loop for (item . rest) on list
    do (format t "~a" item)
    when rest do (format t ", "))

(loop for (a nil) in '((1 2) (3 4) (5 6)) collect a)

(defparameter *random* (loop repeat 100 collect (random 10000)))

(loop for i in *random*
   counting (evenp i) into evens
   counting (oddp i) into odds
   summing i into total
   maximizing i into max
   minimizing i into min
   finally (return (list min max total evens odds)))

(loop for i from 1 to 10 do (print i))

(block outer
  (loop for i from 0 return 100)
  (print "This will print")
  200)

(block outer
  (loop for i from 0 do (return-from outer 100))
  (print "This won't print")
  200)

(loop for i from 1 to 10 do (when (evenp i) (print i)))

(loop for i from 1 to 10 when (evenp i) sum i)

(defvar numbers '(2 4 6 8 10))

(if (loop for n in numbers always (evenp n))
    (print "All numbers even."))

(if (loop for n in numbers never (oddp n))
    (print "All numbers even."))

(loop for char across "abc123" thereis (digit-char-p char))

(loop for char across "abcdef" thereis (digit-char-p char))

Session transcript

The transcript of the test session:

2/8> (loop for i upto 10 collect i)
(0 1 2 3 4 5 6 7 8 9 10)
2/9> 

2/9> (loop for i from 0 downto -10 collect i)
(0 -1 -2 -3 -4 -5 -6 -7 -8 -9 -10)
2/10> 

2/10> (loop for i in (list 10 20 30 40) collect i)
(10 20 30 40)
2/11> 

2/11> (loop for i in (list 10 20 30 40) by #'cddr collect i)
(10 30)
2/12> 

2/12> (loop for x on (list 10 20 30) collect x)
((10 20 30) (20 30) (30))
2/13> 

2/13> (loop for x on (list 10 20 30 40) by #'cddr collect x)
((10 20 30 40) (30 40))
2/14> 

2/14> (loop for x across "abcd" collect x)
(#\a #\b #\c #\d)
2/15> 

2/15> (loop repeat 5 
      for x = 0 then y
      for y = 1 then (+ x y)
      collect y)
Loop form tail (FOR X = 0 THEN Y FOR Y = 1 THEN (+ X Y) COLLECT Y) remained unprocessed.

2/16> 

2/16> (loop repeat 5
      for y = 1 then (+ x y)
      for x = 0 then y
      collect y)
Loop form tail (FOR Y = 1 THEN (+ X Y) FOR X = 0 THEN Y COLLECT Y) remained unprocessed.

2/17> 

2/17> (loop repeat 5 
      for x = 0 then y
      and y = 1 then (+ x y)
      collect y)
Loop form tail (FOR X = 0 THEN Y AND Y = 1 THEN (+ X Y) COLLECT Y) remained unprocessed.

2/18> 

2/18> (loop for (a b) in '((1 2) (3 4) (5 6))
            do (format t "a: ~a; b: ~a~%" a b))
a: 1; b: 2
a: 3; b: 4
a: 5; b: 6
NIL
2/19> 

2/19> (defvar list '(a b c d e))
LIST
2/20> 

2/20> (loop for cons on list
    do (format t "~a" (car cons))
    when (cdr cons) do (format t ", "))
A, B, C, D, E
NIL
2/21> 

2/21> (loop for (item . rest) on list
    do (format t "~a" item)
    when rest do (format t ", "))
A, B, C, D, E
NIL
2/22> 

2/22> (loop for (a nil) in '((1 2) (3 4) (5 6)) collect a)
(1 3 5)
2/23> 

2/23> (defparameter *random* (loop repeat 100 collect (random 10000)))
*RANDOM*
2/24> 

2/24> (loop for i in *random*
   counting (evenp i) into evens
   counting (oddp i) into odds
   summing i into total
   maximizing i into max
   minimizing i into min
   finally (return (list min max total evens odds)))
(50 9951 437975 53 47)
2/25> 

2/25> (loop for i from 1 to 10 do (print i))

1 
2 
3 
4 
5 
6 
7 
8 
9 
10 
NIL
2/26> 

2/26> (block outer
  (loop for i from 0 return 100)
  (print "This will print")
  200)

"This will print" 
200
2/27> 

2/27> (block outer
  (loop for i from 0 do (return-from outer 100))
  (print "This won't print")
  200)
100
2/28> 

2/28> (loop for i from 1 to 10 do (when (evenp i) (print i)))

2 
4 
6 
8 
10 
NIL
2/29> 

2/29> (loop for i from 1 to 10 when (evenp i) sum i)
30
2/30> 

2/30> (defvar numbers '(2 4 6 8 10))
NUMBERS
2/31> 

2/31> (if (loop for n in numbers always (evenp n))
    (print "All numbers even."))

"All numbers even." 
"All numbers even."
2/32> 

2/32> (if (loop for n in numbers never (oddp n))
    (print "All numbers even."))

"All numbers even." 
"All numbers even."
2/33> 

2/33> (loop for char across "abc123" thereis (digit-char-p char))
1
2/34> 

2/34> (loop for char across "abcdef" thereis (digit-char-p char))
NIL
2/35> 

[pamoroso]

PR #1605 addresses the Loop form tail (...) remained unprocessed issue.