Compile Clojure regex literals.

core$simple.class

Classfile /home/mark/src/clj-re/target/classes/clj_re/core$simple.class
  Last modified 13-Jun-2018; size 1119 bytes
  MD5 checksum 7a8f0ea3a3b22a33c335acffef1eda0a
  Compiled from "core.clj"
public final class clj_re.core$simple extends clojure.lang.AFunction
  minor version: 0
  major version: 49
  flags: ACC_PUBLIC, ACC_FINAL, ACC_SUPER
Constant pool:
   #1 = Utf8               clj_re/core$simple
   #2 = Class              #1             // clj_re/core$simple
   #3 = Utf8               clojure/lang/AFunction
   #4 = Class              #3             // clojure/lang/AFunction
   #5 = Utf8               core.clj
   #6 = Utf8               <init>
   #7 = Utf8               ()V
   #8 = NameAndType        #6:#7          // "<init>":()V
   #9 = Methodref          #4.#8          // clojure/lang/AFunction."<init>":()V
  #10 = Utf8               invokeStatic
  #11 = Utf8               (Ljava/lang/Object;)Ljava/lang/Object;
  #12 = Utf8               const__0
  #13 = Utf8               Lclojure/lang/Var;
  #14 = NameAndType        #12:#13        // const__0:Lclojure/lang/Var;
  #15 = Fieldref           #2.#14         // clj_re/core$simple.const__0:Lclojure/lang/Var;
  #16 = Utf8               clojure/lang/Var
  #17 = Class              #16            // clojure/lang/Var
  #18 = Utf8               getRawRoot
  #19 = Utf8               ()Ljava/lang/Object;
  #20 = NameAndType        #18:#19        // getRawRoot:()Ljava/lang/Object;
  #21 = Methodref          #17.#20        // clojure/lang/Var.getRawRoot:()Ljava/lang/Object;
  #22 = Utf8               clojure/lang/IFn
  #23 = Class              #22            // clojure/lang/IFn
  #24 = Utf8               const__1
  #25 = Utf8               Ljava/lang/Object;
  #26 = NameAndType        #24:#25        // const__1:Ljava/lang/Object;
  #27 = Fieldref           #2.#26         // clj_re/core$simple.const__1:Ljava/lang/Object;
  #28 = Utf8               invoke
  #29 = Utf8               (Ljava/lang/Object;Ljava/lang/Object;)Ljava/lang/Object;
  #30 = NameAndType        #28:#29        // invoke:(Ljava/lang/Object;Ljava/lang/Object;)Ljava/lang/Object;
  #31 = InterfaceMethodref #23.#30        // clojure/lang/IFn.invoke:(Ljava/lang/Object;Ljava/lang/Object;)Ljava/lang/Object;
  #32 = Utf8               x
  #33 = NameAndType        #10:#11        // invokeStatic:(Ljava/lang/Object;)Ljava/lang/Object;
  #34 = Methodref          #2.#33         // clj_re/core$simple.invokeStatic:(Ljava/lang/Object;)Ljava/lang/Object;
  #35 = Utf8               <clinit>
  #36 = Utf8               clojure.core
  #37 = String             #36            // clojure.core
  #38 = Utf8               re-find
  #39 = String             #38            // re-find
  #40 = Utf8               clojure/lang/RT
  #41 = Class              #40            // clojure/lang/RT
  #42 = Utf8               var
  #43 = Utf8               (Ljava/lang/String;Ljava/lang/String;)Lclojure/lang/Var;
  #44 = NameAndType        #42:#43        // var:(Ljava/lang/String;Ljava/lang/String;)Lclojure/lang/Var;
  #45 = Methodref          #41.#44        // clojure/lang/RT.var:(Ljava/lang/String;Ljava/lang/String;)Lclojure/lang/Var;
  #46 = Utf8               some.*regex.*literal
  #47 = String             #46            // some.*regex.*literal
  #48 = Utf8               java/util/regex/Pattern
  #49 = Class              #48            // java/util/regex/Pattern
  #50 = Utf8               compile
  #51 = Utf8               (Ljava/lang/String;)Ljava/util/regex/Pattern;
  #52 = NameAndType        #50:#51        // compile:(Ljava/lang/String;)Ljava/util/regex/Pattern;
  #53 = Methodref          #49.#52        // java/util/regex/Pattern.compile:(Ljava/lang/String;)Ljava/util/regex/Pattern;
  #54 = Utf8               Code
  #55 = Utf8               LineNumberTable
  #56 = Utf8               LocalVariableTable
  #57 = Utf8               SourceFile
  #58 = Utf8               SourceDebugExtension
{
  public static final clojure.lang.Var const__0;
    descriptor: Lclojure/lang/Var;
    flags: ACC_PUBLIC, ACC_STATIC, ACC_FINAL

  public static final java.lang.Object const__1;
    descriptor: Ljava/lang/Object;
    flags: ACC_PUBLIC, ACC_STATIC, ACC_FINAL

  public clj_re.core$simple();
    descriptor: ()V
    flags: ACC_PUBLIC
    Code:
      stack=1, locals=1, args_size=1
         0: aload_0
         1: invokespecial #9                  // Method clojure/lang/AFunction."<init>":()V
         4: return
      LineNumberTable:
        line 4: 0

  public static java.lang.Object invokeStatic(java.lang.Object);
    descriptor: (Ljava/lang/Object;)Ljava/lang/Object;
    flags: ACC_PUBLIC, ACC_STATIC
    Code:
      stack=4, locals=1, args_size=1
         0: getstatic     #15                 // Field const__0:Lclojure/lang/Var;
         3: invokevirtual #21                 // Method clojure/lang/Var.getRawRoot:()Ljava/lang/Object;
         6: checkcast     #23                 // class clojure/lang/IFn
         9: getstatic     #27                 // Field const__1:Ljava/lang/Object;
        12: aload_0
        13: aconst_null
        14: astore_0
        15: invokeinterface #31,  3           // InterfaceMethod clojure/lang/IFn.invoke:(Ljava/lang/Object;Ljava/lang/Object;)Ljava/lang/Object;
        20: areturn
      LocalVariableTable:
        Start  Length  Slot  Name   Signature
            0      20     0     x   Ljava/lang/Object;
      LineNumberTable:
        line 4: 0
        line 5: 6
        line 5: 15

  public java.lang.Object invoke(java.lang.Object);
    descriptor: (Ljava/lang/Object;)Ljava/lang/Object;
    flags: ACC_PUBLIC
    Code:
      stack=2, locals=2, args_size=2
         0: aload_1
         1: aconst_null
         2: astore_1
         3: invokestatic  #34                 // Method invokeStatic:(Ljava/lang/Object;)Ljava/lang/Object;
         6: areturn
      LineNumberTable:
        line 4: 3

  public static {};
    descriptor: ()V
    flags: ACC_PUBLIC, ACC_STATIC
    Code:
      stack=2, locals=0, args_size=0
         0: ldc           #37                 // String clojure.core
         2: ldc           #39                 // String re-find
         4: invokestatic  #45                 // Method clojure/lang/RT.var:(Ljava/lang/String;Ljava/lang/String;)Lclojure/lang/Var;
         7: checkcast     #17                 // class clojure/lang/Var
        10: putstatic     #15                 // Field const__0:Lclojure/lang/Var;
        13: ldc           #47                 // String some.*regex.*literal
        15: invokestatic  #53                 // Method java/util/regex/Pattern.compile:(Ljava/lang/String;)Ljava/util/regex/Pattern;
        18: putstatic     #27                 // Field const__1:Ljava/lang/Object;
        21: return
      LineNumberTable:
        line 4: 0
}
SourceFile: "core.clj"
SourceDebugExtension:
  SMAP
  core.java
  Clojure
  *S Clojure
  *F
  + 1 core.clj
  clj_re/core.clj
  *L
  2#1,4:2
  *E

core.clj

(ns clj-re.core
    (:gen-class))

(defn simple [x]
  (re-find #"some.*regex.*literal" x)) ;; this regex ends up as a `static final Pattern ...` in the compiled code

In the compiled code, public static final clojure.lang.Var const__0 ends up as a var containing the clojure.core/re-find function (IFn instance). public static final java.lang.Object const__1 ends up as the compiled Pattern object for #"some.*regex.*literal" (https://gist.github.com/overthink/c9408d72e52a45a2a33015221b551788#file-core-simple-class-L134-L135). So each invocation of simple just references the compiled regex.