Awesome

newest (incomplete) version is code-named 'olmec'. See olmec/README.md .

inca

This document describes the interpreter implemented in inca.c, or inca "1". A revised and expanded version is implemented in inca2.c, and documented in README2.md and in the wiki page.

A third rewrite has begun in inca3.c. Its documentation is (predictably) named README3.md.

The newest (incomplete) version is code-named 'olmec'. See olmec/README.md .

The final two commits of inca.c illustrate the problem inherent in the design. Add the new feature (user-function call without the ' or '' function-call functions) broke the existing code in tea.sh (the "use-case"). And so, the project was begun anew with a better design.

It may surprise or amuse readers to learn that even the earliest inca.c was not my first brush with APL. Some years ago I read a great deal of the J wiki and then could not get it to compile and completely forgot. A few years later, having issued a programming challenge and received a few J answers, I looked again and wrote two postscript programs to simulate what I thought was going on. https://gist.github.com/luser-dr00g/9382217 and https://gist.github.com/luser-dr00g/9502855

And some time later I stumbled upon some very old source code of mine which attempted (anticipated?) a similar arbitrary-dimensional system in C++. https://groups.google.com/d/topic/comp.lang.apl/3VNPOzcQMMI/discussion

Summary: monadic functions: + id { size ~ iota < box # shape > unbox | abs ! not @ rev
dyadic function: + add { from ~ find < assign # reshape , cat ; rowcat - minus . time
* pow % divide | mod & and ^ or = eq / compress \ expand
mon ops: / reduce (.-|/+><)@ transpose dy op: . matrix product
variable ` (backtick) is set to result of the previous command. (was underscore)

An online version is available courtesy of Thomas Baruchel. http://baruchel.hd.free.fr/apps/apl/inca/ which is awesome and even handles cut+paste.

The program is based on and directly derived from the J-incunabulum,
http://www.jsoftware.com/jwiki/Essays/Incunabulum
and extended to allow propagating specifications "a+2+a<3", new functions minus,times,unbox. multi-digit integers. identity element for monadic use of minus,times,cat. Most extensions have been incorporated "ad-hoc", with an attempt to maintain consistency of style, balanced against a need (demand) for more commentary and more visible type identifiers.

The name "inca" was chosen for its similarity to "incunabulum", as well as its obvious (to me) decomposition "In C, A", as well as the apparent similarity between array-structured data and the ancient Incan data-storage device, the quipu. http://en.wikipedia.org/wiki/Quipu

The file inca.c compiles for me with cygwin32 gcc. The code does not consistently adhere to any particular version of the C standard, and may fail to compile with -pedantic, or any other options to enforce standards-conformance.

I first found the J incunabulum through this SO question: http://stackoverflow.com/questions/13827096/how-can-i-compile-and-run-this-1989-written-c-program And I've added links to various explanatory pages as comments to that question, and a bugfix for the original. Here are the helpful links: http://www.jsoftware.com/papers/AIOJ/AIOJ.htm
https://groups.google.com/d/msg/sayeret-lambda/Oxffk3aeUP4/QEuZocgVh5UJ
http://archive.vector.org.uk/trad/v094/hui094_85.pdf

Inca has been submitted for critique on comp.lang.c and and comp.lang.apl. And some of the advice given has been followed. It has not been tested with a 64-bit intptr_t. The code may make 32bit assumptions, although I've tried to be careful not to do this. I may not have been completely succesful. The basis of the interpreter is the ability to treat a pointer as an integer and pack them in the same-sized fields. Additionally, it assumes that pointer values may be distinguished from character values from their integer representations. This assumption is not guaranteed by the standard, but appears empirically to be true on my cygwin and ubuntu gnu linux testbeds. The original code also assumed that these pointer values will be positive, which is empirically not true on cygwin. Not sure about ubuntu, the code was fixed to use abs(intptr) before the range::type comparison well before it was ported.

Inca will also accept command-line arguments into the program. These are available in the 'a' variable as a box-array of command-string arrays. Also included with the distribution is the small lib.inca file which accumulates a few functions that arose in postings to comp.lang.apl. If inca is invoked thusly:

 ./inca `cat lib.inca`

Then the library can be executed by putting the box-array a in a box '<', making it executeable '$', and executing it ';'.

           ;$<a

Which should respond with the friendly message:

 2:11 
 lib_loaded

With the simple code representation of small integers for operators, ascii for variables and other non-operator punctuation, and pointers (boxed arrays, which here are just scalars (array rank=0)), code can be generated and executed on the fly. The r function in lib.inca illustrates this:

 r<:(40.'iy);(1+~<y);((0{:").'iy);((0{:u).'iy);(@~<y);(41.'iy);((0{:;).'iy-1),0

The basic structure here is a series of parenthesized expressions which are strung together with ; (rowcat). (40.'iy) makes a vector of y left parens. (1+<y) makes a boxed iota vector 1..y. (0{:") is the quote literal, used the same way the 40 was for left paren. Since double-quote " is a function, its code representation is not the same as its ascii representation, so we extract it from a short code sequence which starts at the colon and goes until the closing paren, so just the double-quote function. ((0{:u).'iy) is the same, but with the 'u' variable, which could be accessed by ascii, if you want to, or by pulling it out of a short code sequence. (@<y) gives a reversed box iota y-1..0. (41.'iy) is a vector of closing parens. And the final row is y-1 semicolons, and a final terminating null.

This produces the transpose of several expresions (j"uk); with j and k varying. And it can be executed by transposing, ravelling, making executable and then executing. ;$,@ which the s function does.

Executing the s function calls r to generate a procedure to produce a triangular matrices by a run-length encoded representation, built using iotas, directly into the form of function calls to the function u which takes two numbers and produces a row of the matrix.

Functions can also call themselves recursively.

Fibonacci function:

 f<:;(y>1){(<:1);<:('fy-1)+'fy-2

Factorial function:

 f<:;(y>1){(<:1);<:y.fy-1

In the run-length-encoded triangular matrix example, the rows were all the same length, so rowcat has an easy time to combine rows. But here, the two code sequences

 :1
 :('fy-1)+'fy-2

are different lengths. So we box them, so rowcat doesn't screw things up. (FIXME: fix rowcat to pad unequal widths).

 <:1
 <:('fy-1)+'fy-2

rowcat them together ((...);...), select one using a boolean expression (y>1){, and execute the resulting expression ;.

And also not executing a command-string prints the string, so:

    :Hello World!
Hello World!

Recalling the syntax for executing code from the command-line.

   ;$<a

This illustrates a means by which "multi-line" functions may be conveniently constructed, via a confusing arrangement of vaguely-defined concepts like "box" and "box-array". The text lines of the file from cat file are, again, defined in the variable a as a box-array, an array of pointers, of command-strings. To execute the box-array as a whole, it must be put into a single box. (Errmm. This feels like an artificial restriction, and it is with difficulty that I document the current behavior of the implementation here...)

Following this pattern, one might define a multi-statement function in the same manner, as an executable box of a box-array of command strings.

    f<$<(<:a<1);(<:b<2);(<:c<3)

Executing ;f should then be equivalent to the separate statements.

    a<1
    b<2
    c<3

Implements monadic functions m mW

 + identity   +1  =>  1
 { size      1 1 1  =>  3
 ~ iota       ~9   =>   0 1 2 3 4 5 6 7 8
 < box        <1 1 1  =>   <1 1 1  (bad example)
 # shape      #~9  =>  9
 > unbox      ><1 1 1  =>   1 1 1
 | absolute    |-12   =>   12
 ! not         !0 1 0   =>   1 0 1
 @ reverse     @~9    =>   8 7 6 5 4 3 2 1 0
 : yield array of remaining command string
 ; execute command string array
 $ convert array to command-string type
 'w  call function w with y as right arg
     function may be a variable containing code (with colon :), eg. square
         s<:y.y
         's6
    36
     or a parenthesized expression, without colon :
         '(y.y)6
    36

dyadic functions d AdW

 + plus
 { from       2 3{@~9   =>   6 5
 ~ find       6 5~@~9   =>   2 3
 < assign if a is a var (not really a function, but an interpreter action) 
 # reshape
 , cat 
 ; rowcat
 - minus   (monadic: a=0)
 . times   (monadic: a=1)
 * power   (monadic: a=2)  <-- this will be e with floating-point
 % divide  (monadic: a=1)  <-- this will make more sense with floating-point
 | modulus   (reverse of C: w%a, divisor on the right)
 & and 
 ^ or 
 = equals?
 ! not-equal?
 : match
 < less-than   (if a is not a var, see assign above)
 / compress
 \ expand
 "w  call function w with x as left arg and y as right arg
     function may be a variable containing code (with colon :), eg x+1-y
         f<:x+1-y
         3"f2
    2
     or a parenthesized expression, without colon :
         3"(x+1-y)2
    2

monadic operators

 / reduce  f/W  => w0 f (w1 f (w2 f ( ... wn-2 f wn-1)))
 \ scan    f\W  => (w0 f w1), ((w0 f w1) f w2), ... ) f wn-2) f wn-1)
 @ transpose   .@  identity transpose
               -@  vertical transpose
               |@  horizontal transpose
               \@  y=x transpose
               /@  y=-x transpose
               +@  horz then vert
               >@  horz then y=x
               <@  horz then y=-x

dyadic operator

 . matrix product Af.gW => f/Ag\@W
   ( @ for the left function designates "jot-dot", a null-scan over the matrix product )
    eg. plus over times:       +..
        plus over plus:        +.+
        addition table:        @.+
        multiplication table:  @..

over multidigit numbers and variables
<pre>`</pre> (backtick), and [a-z]

<pre>`</pre> (backtick) is set to the result of the previous line. (was underscore)

The interpreter also implements a non-greedy "cat" for number vectors separated by spaces. Hence 1 2 3+~3 => 1 3 5 where ~ is the zero-based iota. Spaces must only be used between numbers. You may not pad operators with extra space or it will be misinterpreted.

If the length of the command string exceeds 998 characters, the behavior is undefined.

If array operands have incompatible sizes, the behavior is undefined.

Example sessions:

monadic functions.

josh@Z1 ~/inca
$ !.
./inca
        +5

5 
        {1 2 3
1 
3 
        ~9
9 
0 1 2 3 4 5 6 7 8 
        ~0
0 

        <12

< 
12 
        #1 2 3;4 5 6
2 
2 3 
        |-25

25 
        !4

0 
        !0

1 
        \@1 2 3;4 5 6;7 8 9;10 11 12
3 4 
1 4 7 10 
2 5 8 11 
3 6 9 12 
        \@4 3#1+~12
3 4 
1 4 7 10 
2 5 8 11 
3 6 9 12 
        @`
3 4 
12 9 6 3 
11 8 5 2 
10 7 4 1 

josh@Z1 ~/inca
$

Example session: dyadic functions and operators.
(output has been augmented with a type-specifier then colon : then dims)

$ ./inca
        2 3+7 6
0:2 
9 9 
        1{52 53 54
0:
53 
        5~4+~9
0:
1 
        4+~9
0:9 
4 5 6 7 8 9 10 11 12 
        a<10
0:
10 
        b+a+b<6
0:
22 
        b
0:
6 
        ~64
0:64 
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 
        8 8#`
0:8 8 
0 1 2 3 4 5 6 7 
8 9 10 11 12 13 14 15 
16 17 18 19 20 21 22 23 
24 25 26 27 28 29 30 31 
32 33 34 35 36 37 38 39 
40 41 42 43 44 45 46 47 
48 49 50 51 52 53 54 55 
56 57 58 59 60 61 62 63 
        `,~9
0:73 
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 0 1 2 3 4 5 6 7 8 
        12 6#`
0:12 6 
0 1 2 3 4 5 
6 7 8 9 10 11 
12 13 14 15 16 17 
18 19 20 21 22 23 
24 25 26 27 28 29 
30 31 32 33 34 35 
36 37 38 39 40 41 
42 43 44 45 46 47 
48 49 50 51 52 53 
54 55 56 57 58 59 
60 61 62 63 0 1 
2 3 4 5 6 7 
        5.-2
0:
-10 
        2*3
0:
8 
        3*2
0:
9 
        *3
0:
8 
        **3
0:
256 
        2*2*3
0:
256 
        +/~9
0:
36 
        ./~9
0:
0 
        ./1+~9
0:
362880 
        ./1+~4
0:
24 
        1.2.3.4
0:
24 
        1 2 3 4+..5 6 7 8
0:
70 
        1.5
0:
5 
        `+2.6
0:
17 
        `+3.7
0:
38 
        `+4.8
0:
70

Example session: general transpose operator.