A generic way to define function that cache their values.

)abbrev domain CACHEDF CachedFunction                                             
++ Author: Ralf Hemmecke                                                          
++ Date Created: 2009                                                             
++ Date Last Updated: Oct 27, 2009                                                
++ Basic Operations:                                                              
++ Related Domains: Table, AssociationList                                        
++ Also See:                                                                      
++ AMS Classifications:
++ Keywords:
++ Examples:
++ References:
++ Description:
++   This domain is a domain of functions with associated cache.
CachedFunction(A: SetCategory, B: SetCategory): Exports == Implementation where
    Exports ==> with
        function: % -> (A -> B)
        cachedFunction: (A -> B) -> %
        apply: (%, A) -> B
        recursiveDefine: (%, f: A -> B) -> %

    Implementation ==> add

        Rep := Record(cache: Table(A, B), fun: A -> B);

        function(x: %): A -> B == x.fun

        cachedFunction(f: A -> B): % == [empty()$Table(A, B), f]

        apply(x: %, a: A): B ==
            c := x.cache
            u: Union(B, "failed") := search(a, c)
            if u case B
               then u :: B
               else
                 f: A -> B := x.fun
                 c.a := f(a)

        recursiveDefine(x: %, f: A -> B): % ==
            x.fun := f;
            x

   Compiling FriCAS source code from file 
      /var/lib/zope2.10/instance/axiom-wiki/var/LatexWiki/8303643491408128431-25px001.spad
      using old system compiler.
   CACHEDF abbreviates domain CachedFunction 
------------------------------------------------------------------------
   initializing NRLIB CACHEDF for CachedFunction 
   compiling into NRLIB CACHEDF 
   compiling exported function : $ -> A -> B
      CACHEDF;function;$M;1 is replaced by QCDR 
Time: 0 SEC.

   compiling exported cachedFunction : A -> B -> $
Time: 0 SEC.

   compiling exported apply : ($,A) -> B
Time: 0.01 SEC.

   compiling exported recursiveDefine : ($,A -> B) -> $
Time: 0 SEC.

(time taken in buildFunctor:  0)

;;;     ***       |CachedFunction| REDEFINED

;;;     ***       |CachedFunction| REDEFINED
Time: 0 SEC.

   Warnings: 
      [1] function:  fun has no value
      [2] apply:  cache has no value
      [3] apply:  fun has no value
      [4] recursiveDefine:  fun has no value

   Cumulative Statistics for Constructor CachedFunction
      Time: 0.01 seconds

   finalizing NRLIB CACHEDF 
   Processing CachedFunction for Browser database:
--------constructor---------
--->-->CachedFunction((function ((Mapping B A) %))): Not documented!!!!
--->-->CachedFunction((cachedFunction (% (Mapping B A)))): Not documented!!!!
--->-->CachedFunction((apply (B % A))): Not documented!!!!
--->-->CachedFunction((recursiveDefine (% % (Mapping B A)))): Not documented!!!!
; compiling file "/var/aw/var/LatexWiki/CACHEDF.NRLIB/CACHEDF.lsp" (written 04 APR 2022 07:27:27 PM):

; /var/aw/var/LatexWiki/CACHEDF.NRLIB/CACHEDF.fasl written
; compilation finished in 0:00:00.028
------------------------------------------------------------------------
   CachedFunction is now explicitly exposed in frame initial 
   CachedFunction will be automatically loaded when needed from 
      /var/aw/var/LatexWiki/CACHEDF.NRLIB/CACHEDF

)set message time on

I := Integer

(1)

Time: 0.02 (OT) = 0.02 sec
f(n:I): I ==1

   Function declaration f : Integer -> Integer has been added to 
      workspace.

Time: 0 sec
fib: CachedFunction(I,I) := cachedFunction(f)

Compiling function f with type Integer -> Integer 

 LISP output:
(#<HASH-TABLE :TEST EQUAL :COUNT 0 {10051A83F3}> #<FUNCTION |*1;f;1;initial|>)

Time: 0.01 (OT) = 0.01 sec
recursiveDefine(fib,(n:I):I+->if n<2 then 1 else fib(n-1) + fib(n-2))

 LISP output:
(#<HASH-TABLE :TEST EQUAL :COUNT 0 {10051A83F3}> #<FUNCTION |*1;anonymousFunction;0;initial;internal|>)

Time: 0.01 (IN) = 0.01 sec
fib 40

(2)

Time: 0.01 (IN) = 0.01 sec
g(n:I): I == if n<2 then 1 else g(n-1)+g(n-2)

   Function declaration g : Integer -> Integer has been added to 
      workspace.

Time: 0 sec
g 40

Compiling function g with type Integer -> Integer

(3)

Time: 3.32 (EV) = 3.32 sec
h: I -> I := function fib

(4)

Time: 0 sec
h 40

(5)

Time: 0 sec

)set message time off

Caching a function with more than one argument

We need to combine more than one domain into a single domain in a universal manner like a cross-product. There are seveal ways to do this in Axiom including List, Record, Product and DirectProduct. For example:

-- combine two domain in one using Record
Pair:=Record(x1:Integer,x2:Integer)

(6)

pair(x:Integer,y:Integer):Pair == [x,y]

   Function declaration pair : (Integer, Integer) -> Record(x1: Integer
      ,x2: Integer) has been added to workspace.

--
gcd2(arg:Pair):Integer == gcd(arg.x1,arg.x2)

   Function declaration gcd2 : Record(x1: Integer,x2: Integer) -> 
      Integer has been added to workspace.

gcd2cached:CachedFunction(Pair,Integer):=cachedFunction gcd2

Compiling function gcd2 with type Record(x1: Integer,x2: Integer)
       -> Integer 

 LISP output:
(() #<FUNCTION |*1;gcd2;1;initial|>)

gcdCached(x1:Integer,x2:Integer):Integer == gcd2cached pair(x1,x2)

   Function declaration gcdCached : (Integer, Integer) -> Integer has 
      been added to workspace.

)set message time on

for i in 1..100 repeat for j in 1..100 repeat gcd(i,j)

Time: 0.33 (EV) = 0.33 sec
for i in 1..100 repeat for j in 1..100 repeat gcdCached(i,j)

Compiling function pair with type (Integer, Integer) -> Record(x1: 
      Integer,x2: Integer)

Compiling function gcdCached with type (Integer, Integer) -> Integer

Time: 0.01 (IN) + 7.09 (EV) = 7.10 sec

)set message time off

testhash() ==
  for i in 1..100 repeat for j in 1..100 repeat
    if gcdCached(i,j)~=gcd(i,j) then error "bad hash!"
  "good"

testhash()

Compiling function testhash with type () -> String

(7)

I was rather disappointed with the performance of the cache! So I took a look at the source code for Table and it seems that Table only uses an efficient hashing method if hashable(Key)$Lisp is true, where Key is the first domain of Table(Key,Entry). This is true for Integer and String but not Record(x1:Integer,x2:Integer) or even List(Integer).

hashable(Integer)$Lisp

(8)

hashable(String)$Lisp

(9)

hashable(Record(x1:Integer,x2:Integer))$Lisp

   Compiled code for gcd2 has been cleared.

(10)

hashable(List Integer)$Lisp

(11)

But as far as I can see the implementation of List and Record in Axiom do satisfy the requirements for the use of HashTable?:

  ++   This creates a \spadtype{HashTable} if equal for the Key
  ++   domain is consistent with Lisp EQUAL otherwise an
  ++   \spadtype{AssociationList}

if their component domains do. So I think it would be a good idea to make the hashable function in 'spad.lisp':

  (defun |knownEqualPred| (dom)
    (let ((fun (|compiledLookup| '= '((|Boolean|) $ $) dom)))
      (if fun (get (bpiname (car fun)) '|SPADreplace|)
        nil)))

  (defun |hashable| (dom)
    (memq (|knownEqualPred| dom)
          #-Lucid '(EQ EQL EQUAL)
          #+Lucid '(EQ EQL EQUAL EQUALP)
          ))

a little smarter. This test only seems to check if the compiler was able to optimize equality to a lisp operator. I suppose we could improve the compiler but even failing that, there should be a way to recognize it at this level. I think it's something like having the Canonical property "all the way down".

)clear completely

   All user variables and function definitions have been cleared.
   All )browse facility databases have been cleared.
   Internally cached functions and constructors have been cleared.
   )clear completely is finished.

We can test this for now by using HashTable? explicitly and just assuming that that domain A satisfies the requirement:

)abbrev domain CACHEDF CachedFunction                                             
CachedFunction(A: SetCategory, B: SetCategory): Exports == Implementation where
    Exports ==> with
        function: % -> (A -> B)
        cachedFunction: (A -> B) -> %
        apply: (%, A) -> B
        recursiveDefine: (%, f: A -> B) -> %

    Implementation ==> add

        Rep := Record(cache: HashTable(A, B, "UEQUAL"), fun: A -> B);

        function(x: %): A -> B == x.fun

        cachedFunction(f: A -> B): % == [empty()$HashTable(A, B, "UEQUAL"), f]

        apply(x: %, a: A): B ==
            c := x.cache
            u: Union(B, "failed") := search(a, c)
            if u case B
               then u :: B
               else
                 f: A -> B := x.fun
                 c.a := f(a)

        recursiveDefine(x: %, f: A -> B): % ==
            x.fun := f;
            x

   Compiling FriCAS source code from file 
      /var/lib/zope2.10/instance/axiom-wiki/var/LatexWiki/6894297888104578709-25px008.spad
      using old system compiler.
   CACHEDF abbreviates domain CachedFunction 
------------------------------------------------------------------------
   initializing NRLIB CACHEDF for CachedFunction 
   compiling into NRLIB CACHEDF 
Local variable Rep type redefined: (Join (SetCategory) (CATEGORY domain (SIGNATURE construct ((Record (: cache (HashTable A B UEQUAL)) (: fun (Mapping B A))) (HashTable A B UEQUAL) (Mapping B A))) (SIGNATURE ~= ((Boolean) (Record (: cache (HashTable A B UEQUAL)) (: fun (Mapping B A))) (Record (: cache (HashTable A B UEQUAL)) (: fun (Mapping B A))))) (SIGNATURE coerce ((OutputForm) (Record (: cache (HashTable A B UEQUAL)) (: fun (Mapping B A))))) (SIGNATURE elt ((HashTable A B UEQUAL) (Record (: cache (HashTable A B UEQUAL)) (: fun (Mapping B A))) cache)) (SIGNATURE elt ((Mapping B A) (Record (: cache (HashTable A B UEQUAL)) (: fun (Mapping B A))) fun)) (SIGNATURE setelt! ((HashTable A B UEQUAL) (Record (: cache (HashTable A B UEQUAL)) (: fun (Mapping B A))) cache (HashTable A B UEQUAL))) (SIGNATURE setelt! ((Mapping B A) (Record (: cache (HashTable A B UEQUAL)) (: fun (Mapping B A))) fun (Mapping B A))) (SIGNATURE copy ((Record (: cache (HashTable A B UEQUAL)) (: fun (Mapping B A))) (Record (: cache (HashTable A B UEQUAL)) (: fun (Mapping B A))))))) to (Join (SetCategory) (CATEGORY domain (SIGNATURE construct ((Record (: cache (Table A B)) (: fun (Mapping B A))) (Table A B) (Mapping B A))) (SIGNATURE ~= ((Boolean) (Record (: cache (Table A B)) (: fun (Mapping B A))) (Record (: cache (Table A B)) (: fun (Mapping B A))))) (SIGNATURE coerce ((OutputForm) (Record (: cache (Table A B)) (: fun (Mapping B A))))) (SIGNATURE elt ((Table A B) (Record (: cache (Table A B)) (: fun (Mapping B A))) cache)) (SIGNATURE elt ((Mapping B A) (Record (: cache (Table A B)) (: fun (Mapping B A))) fun)) (SIGNATURE setelt! ((Table A B) (Record (: cache (Table A B)) (: fun (Mapping B A))) cache (Table A B))) (SIGNATURE setelt! ((Mapping B A) (Record (: cache (Table A B)) (: fun (Mapping B A))) fun (Mapping B A))) (SIGNATURE copy ((Record (: cache (Table A B)) (: fun (Mapping B A))) (Record (: cache (Table A B)) (: fun (Mapping B A)))))))
   compiling exported function : $ -> A -> B
      CACHEDF;function;$M;1 is replaced by QCDR 

;;;     ***       |CACHEDF;function;$M;1| REDEFINED
Time: 0 SEC.

   compiling exported cachedFunction : A -> B -> $

;;;     ***       |CACHEDF;cachedFunction;M$;2| REDEFINED
Time: 0.01 SEC.

   compiling exported apply : ($,A) -> B

;;;     ***       |CACHEDF;apply;$AB;3| REDEFINED
Time: 0 SEC.

   compiling exported recursiveDefine : ($,A -> B) -> $

;;;     ***       |CACHEDF;recursiveDefine;$M$;4| REDEFINED
Time: 0 SEC.

(time taken in buildFunctor:  0)

;;;     ***       |CachedFunction| REDEFINED

;;;     ***       |CachedFunction| REDEFINED
Time: 0 SEC.

   Warnings: 
      [1] function:  fun has no value
      [2] apply:  cache has no value
      [3] apply:  fun has no value
      [4] recursiveDefine:  fun has no value

   Cumulative Statistics for Constructor CachedFunction
      Time: 0.01 seconds

   finalizing NRLIB CACHEDF 
   Processing CachedFunction for Browser database:
--->/var/lib/zope2.10/instance/axiom-wiki/var/LatexWiki/8303643491408128431-25px001.spad-->CachedFunction(constructor): Not documented!!!!
--->/var/lib/zope2.10/instance/axiom-wiki/var/LatexWiki/8303643491408128431-25px001.spad-->CachedFunction((function ((Mapping B A) %))): Not documented!!!!
--->/var/lib/zope2.10/instance/axiom-wiki/var/LatexWiki/8303643491408128431-25px001.spad-->CachedFunction((cachedFunction (% (Mapping B A)))): Not documented!!!!
--->/var/lib/zope2.10/instance/axiom-wiki/var/LatexWiki/8303643491408128431-25px001.spad-->CachedFunction((apply (B % A))): Not documented!!!!
--->/var/lib/zope2.10/instance/axiom-wiki/var/LatexWiki/8303643491408128431-25px001.spad-->CachedFunction((recursiveDefine (% % (Mapping B A)))): Not documented!!!!
--->/var/lib/zope2.10/instance/axiom-wiki/var/LatexWiki/8303643491408128431-25px001.spad-->CachedFunction(): Missing Description
; compiling file "/var/aw/var/LatexWiki/CACHEDF.NRLIB/CACHEDF.lsp" (written 04 APR 2022 07:27:42 PM):

; /var/aw/var/LatexWiki/CACHEDF.NRLIB/CACHEDF.fasl written
; compilation finished in 0:00:00.025
------------------------------------------------------------------------
   CachedFunction is now explicitly exposed in frame initial 
   CachedFunction will be automatically loaded when needed from 
      /var/aw/var/LatexWiki/CACHEDF.NRLIB/CACHEDF

Now let's try that again.

-- combine two domain in one
Pair:=Record(x1:Integer,x2:Integer)

(12)

pair(x:Integer,y:Integer):Pair == [x,y]

   Function declaration pair : (Integer, Integer) -> Record(x1: Integer
      ,x2: Integer) has been added to workspace.

--
gcd2(arg:Pair):Integer == gcd(arg.x1,arg.x2)

   Function declaration gcd2 : Record(x1: Integer,x2: Integer) -> 
      Integer has been added to workspace.

gcd2cached:CachedFunction(Pair,Integer):=cachedFunction gcd2

Compiling function gcd2 with type Record(x1: Integer,x2: Integer)
       -> Integer 

 LISP output:
(#<HASH-TABLE :TEST EQUAL :COUNT 0 {1004DE5253}> #<FUNCTION |*1;gcd2;1;initial|>)

gcdCached(x1:Integer,x2:Integer):Integer == gcd2cached pair(x1,x2)

   Function declaration gcdCached : (Integer, Integer) -> Integer has 
      been added to workspace.

)set message time on

for i in 1..100 repeat for j in 1..100 repeat gcd(i,j)

Time: 0.28 (EV) = 0.28 sec
for i in 1..100 repeat for j in 1..100 repeat gcdCached(i,j)

Compiling function pair with type (Integer, Integer) -> Record(x1: 
      Integer,x2: Integer)

Compiling function gcdCached with type (Integer, Integer) -> Integer

Time: 0.01 (IN) + 0.22 (EV) = 0.23 sec

)set message time off

testhash() ==
  for i in 1..100 repeat for j in 1..100 repeat
    if gcdCached(i,j)~=gcd(i,j) then error "bad hash!"
  "good"

testhash()

Compiling function testhash with type () -> String

(13)

)set message time on
 

)lib CACHEDF

   CachedFunction is already explicitly exposed in frame initial 
   CachedFunction will be automatically loaded when needed from 
      /var/aw/var/LatexWiki/CACHEDF.NRLIB/CACHEDF
fib2: CachedFunction(INT,INT):= cachedFunction (n+->
    if n<2 then 1 else fib2(n-1)+fib2(n-2)
  )

 LISP output:
(#<HASH-TABLE :TEST EQUAL :COUNT 0 {1007D93353}> #<FUNCTION |*1;anonymousFunction;1;initial;internal|>)

Time: 0.01 (OT) = 0.01 sec
fib2 40

(14)

Time: 0.01 (IN) = 0.01 sec

Looks like the time difference (if any) is not significant.