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Comment by lispm | Hacker News Reader

> So reduce can be obviated by just letting the function take variable args too.

In Common Lisp the max number of arguments can be small.

  $ abcl
  Armed Bear Common Lisp 1.8.0
  Java 11.0.19 Ubuntu
  OpenJDK 64-Bit Server VM
  Low-level initialization completed in 0.304 seconds.
  Startup completed in 1.501 seconds.
  Type ":help" for a list of available commands.

  CL-USER(1): CALL-ARGUMENTS-LIMIT
  50

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Interesting. Do you know if that is due to constraints coming from ABCL running on a JVM, or is it an arbitrary choice ? (By contrast, SBCL on a x86_64 laptop returns 4611686018427387903...)

Usually these limits are based on the capabilities of the underlying platform (like the JVM) or the implementation choice. One of the goals is to have fast function calls and less so to have long arguments lists. Less than 2^16 isn't that rare. SBCL is more on the large side. Implementations like ABCL, CLISP and some others have much smaller max arglist length limits.

Don't use

  (apply #'+ long-list-of-numbers)

but use

  (reduce #'+ long-list-of-numbers)

So this wasn't what I was expecting.

  * (disassemble (lambda () (apply #'+ '(1 2 3 4 5))))
  ; disassembly for (LAMBDA ())
  ; Size: 21 bytes. Origin: #x5345C11B                          ; (LAMBDA ())
  ; 1B:       498B4510         MOV RAX, [R13+16]                ; thread.binding-stack-pointer
  ; 1F:       488945F8         MOV [RBP-8], RAX
  ; 23:       BA1E000000       MOV EDX, 30
  ; 28:       488BE5           MOV RSP, RBP
  ; 2B:       F8               CLC
  ; 2C:       5D               POP RBP
  ; 2D:       C3               RET
  ; 2E:       CC10             INT3 16                          ; Invalid argument count trap
  NIL
  * (disassemble (lambda () (reduce #'+ '(1 2 3 4 5))))
  ; disassembly for (LAMBDA ())
  ; Size: 21 bytes. Origin: #x5345C1AB                          ; (LAMBDA ())
  ; AB:       498B4510         MOV RAX, [R13+16]                ; thread.binding-stack-pointer
  ; AF:       488945F8         MOV [RBP-8], RAX
  ; B3:       BA1E000000       MOV EDX, 30
  ; B8:       488BE5           MOV RSP, RBP
  ; BB:       F8               CLC
  ; BC:       5D               POP RBP
  ; BD:       C3               RET
  ; BE:       CC10             INT3 16                          ; Invalid argument count trap
  NIL

There is some SBCL compiler optimizer at work.

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