cplisp

A Lisp that is able to compile part of itself into the constant pool of a Java .class

It uses the new constant dynamic (condy) constant pool constant, so if you want to run the generated classfile, you need either to get an early access build of jdk 11, you can download it at http://jdk.java.net/11/ or you can use pro that embeds its own jdk (see below).

how to build it

I use pro to build the project, Maven can be used to download and run pro, so

  mvn install

it will pack the Java VM and cplisp inside a folder cplisp.

You only need to run Maven once, after that you can use pro directly

  ./pro/bin/pro

how to run cplisp

  ./cplisp/bin/cplisp

the builtin functions are read, print, eval, +, def, lambda, import and compile.

how to compile a script as a Java class

first run cplisp, then ask to compile with the function compile

  (compile foo (print hello cplisp))

it will create a self contained class foo.class on the disk

then you can run the generated foo.class either using the jdk 11

  /path/to/jdk11/bin/java foo

or using pro (which embeds its own jdk)

  ./pro/bin/java foo

Using javap, you can see how the expressions are encoded in the constant pool

  /path/to/jdk11/bin/javap -verbose -c foo.class

  ...
  #14 = String             #13            // cplisp
  #15 = Utf8               fr/umlv/cplisp/CpLisp
  #16 = Class              #15            // fr/umlv/cplisp/CpLisp
  #17 = Utf8               bsm
  #18 = Utf8               (Ljava/lang/invoke/MethodHandles$Lookup;Ljava/lang/String;Ljava/lang/Class;Ljava/lang/Object;[Ljava/lang/Object;)Ljava/lang/Object;
  #19 = NameAndType        #17:#18        // bsm:(Ljava/lang/invoke/MethodHandles$Lookup;Ljava/lang/String;Ljava/lang/Class;Ljava/lang/Object;[Ljava/lang/Object;)Ljava/lang/Object;
  #20 = Methodref          #16.#19        // fr/umlv/cplisp/CpLisp.bsm:(Ljava/lang/invoke/MethodHandles$Lookup;Ljava/lang/String;Ljava/lang/Class;Ljava/lang/Object;[Ljava/lang/Object;)Ljava/lang/Object;
  #21 = MethodHandle       6:#20          // REF_invokeStatic fr/umlv/cplisp/CpLisp.bsm:(Ljava/lang/invoke/MethodHandles$Lookup;Ljava/lang/String;Ljava/lang/Class;Ljava/lang/Object;[Ljava/lang/Object;)Ljava/lang/Object;
  #22 = Utf8               Ljava/lang/Object;
  #23 = NameAndType        #9:#22         // print:Ljava/lang/Object;
  #24 = ConstantDynamic    #0:#23         // #0:print:Ljava/lang/Object;
  #25 = NameAndType        #7:#22         // eval:Ljava/lang/Object;
  #26 = ConstantDynamic    #1:#25         // #1:eval:Ljava/lang/Object;
  #27 = Utf8               Code
  #28 = Utf8               BootstrapMethods
{
  public static void main(java.lang.String[]);
    descriptor: ([Ljava/lang/String;)V
    flags: (0x0009) ACC_PUBLIC, ACC_STATIC
    Code:
      stack=1, locals=1, args_size=1
         0: ldc           #26                 // ConstantDynamic #1:eval:Ljava/lang/Object;
         2: pop
         3: return
}
BootstrapMethods:
  0: #21 REF_invokeStatic fr/umlv/cplisp/CpLisp.bsm:(Ljava/lang/invoke/MethodHandles$Lookup;Ljava/lang/String;Ljava/lang/Class;Ljava/lang/Object;[Ljava/lang/Object;)Ljava/lang/Object;
    Method arguments:
      #10 print
      #12 hello
      #14 cplisp
  1: #21 REF_invokeStatic fr/umlv/cplisp/CpLisp.bsm:(Ljava/lang/invoke/MethodHandles$Lookup;Ljava/lang/String;Ljava/lang/Class;Ljava/lang/Object;[Ljava/lang/Object;)Ljava/lang/Object;
    Method arguments:
      #8 eval
      #24 #0:print:Ljava/lang/Object;

One interesting thing is that by default (thanks to ASM) common sub expressions will be encoded only once in the constant pool. Which mean that the execution of any functions is considered as side effect free, so by example, the following code will print 5 only once

  (compile foo (def a 5) (print a) (def a 7) (print a))

because the second call to (print a) will return the previously calculated value of (print a) without calling print.

So this semantics will only work well for lisps like Clojure that disallow side effect. The other solution is to change the compiler to generate a new constant if there is a side effect, with the function print renamed as print! so it's easy to make the difference between a function which has side effect or not.