ABAP Scheme
The code can be cloned with ABAP GIT.
To check your installation, execute this guess my number game...
(begin (display "Please enter a number between 1 - 100: ")
(do ((quit #f)
(guess 0)
(answer (+ 1 (random 100))) )
(quit)
(begin (set! guess (read)) (display guess) )
(cond ((and (number? guess) (< guess answer)) (display "\nToo low. Please guess again: ") )
((and (number? guess) (> guess answer)) (display "\nToo high. Please guess again: ") )
(else (set! quit #t) (if (number? guess) (display "\nCorrect!")
(display "\nGood bye...") ) ) ) ) )
Scheme syntax is based upon nested parenthesization. The wiki pages are a good place to start.
Scheme's uses symbolic expressions (S-exps) to represent code and data. Expressions are then evaluated. Those concepts cannot be expressed in ABAP, except by first implementing a Lisp interpreter in ABAP (Greenspun 10th rule ).
My initial plan was to write a Lisp workbench for Martin's Lisp interpreter. I changed the target language after reading the Revised 7 Report on the Algorithmic Language Scheme aka R7RS small that offers a lot of examples to verify the interpreter. With this I can aim at compatibility with open source Scheme code.
In constrast to ABAP, Scheme has a very small number of rules for forming expressions that can be composed without restrictions. Scheme is lexically scoped and requires proper tail call optimization. Scheme is apt at symbolic processing.
| S-expression for (* 2 (+ 3 4)) | workbench view |
|---|---|
 |  |
Class lcl_lisp_interpreter evaluates your Scheme code in a string code, using either method eval_repl( code ) which throws an exception on errors, or method eval_source( code ) catches exception:
DATA(response) = NEW lcl_lisp_interpreter( io_port = port
ii_log = log )->eval_source( code ).
port is a buffered port that can allow input or output. log implements a simple logging interface with 2 methods, put( ) and get( ).
For a dynamic IF statement
( PLAAB = '02' ) and ( DELKZ = 'BB') and ( LIFNR > '' ) and ( PLUMI = '-')
we concatenate the following Scheme expression in a string variable code and evaluate.
(let
; Define local fields
((PLAAB (ab-data "GS_MDPS-PLAAB" ))
(DELKZ (ab-data "GS_MDPS-DELKZ" ))
(LIFNR (ab-data "GS_MDPS-LIFNR" ))
(PLUMI (ab-data "GS_MDPS-PLUMI" )))
(and (= PLAAB '02') (= DELKZ 'BB') (> LIFNR '') (= PLUMI '-')) )
The result on the expression either #t or #f.
(let (( profiles
(let ( (f3 (ab-function "BAPI_USER_GET_DETAIL")) )
( begin (ab-set f3 "USERNAME" (ab-get ab-sy "UNAME") ) ; param USERNAME = sy-uname
(f3) ; function module call
(ab-get f3 "PROFILES") ) ) ; return table PROFILES
) )
(let ((profile (ab-get profiles 1)) ) ; read table PROFILES index 1 INTO profile
(ab-get profile "BAPIPROF" ) ) ) ; read field profile-bapiprof
INTERFACE lif_input_port.
METHODS read IMPORTING iv_title TYPE string OPTIONAL
RETURNING VALUE(rv_input) TYPE string.
METHODS peek_char RETURNING VALUE(rv_char) TYPE char01.
METHODS is_char_ready RETURNING VALUE(rv_flag) TYPE flag.
METHODS read_char RETURNING VALUE(rv_char) TYPE char01.
METHODS put IMPORTING iv_text TYPE string.
ENDINTERFACE.
INTERFACE lif_output_port.
METHODS write IMPORTING element TYPE REF TO lcl_lisp.
METHODS display IMPORTING element TYPE REF TO lcl_lisp
RAISING lcx_lisp_exception.
ENDINTERFACE.
Read the ABAP Scheme announcement blog