dadof7/lisp-and-yacc

simple lisp front-end for a yacc generated parser, mini lisp, AST as a list

Lisp front-end for a yacc generated parser

I wanted a lisp front-end for a yacc generated parser so that I can do semantic analysis using lists. Another lisp again? Sorry, yes it is.

This lisp is a simple straight forward implementation based on the work of Yuumi Yoshida at ey-office.com. I got a permission to use the code listed below.

https://atmarkit.itmedia.co.jp/ait/articles/0810/31/news148.html

By assigning values to $$'s, we can get results as lists. Once we got AST as a list, we can massage it in whatever way we like.

From REPL, we can call the parser by evaluating (parse "input.txt") . However syntax and lexical analysis stuff are hard coded into yacc and lex files. Every time you change your grammar, you have to recompile the whole entire things by make. That is OK for my purpose, but it may bother other people.

Example

Included yacc.y describes SQL create table statement. Suppose we have the following code in k.sql.

create table tmEmp (                                            -- master table for employees
        idno                    decimal(15,0) not null      
                                default autoincrement,
        code                    varchar(5) not null,            
        nm                      varchar(40) not null,           
        zip                     varchar(10),                    
        addr                    varchar(80),                    
        phone                   varchar(20),                    
        cellphone               varchar(20),                    
        del                     char(1) not null,               -- delete flg
        primary key(idno)
)

Evaluating (parse "k.sql") yields

((tmEmp
  (idno (:type decimal 15 . 0) (:not-null . t) (:autoincrement . t))
  (code (:type varchar . 5) (:not-null . t))
  (nm (:type varchar . 40) (:not-null . t))
  (zip (:type varchar . 10))
  (addr (:type varchar . 80))
  (phone (:type varchar . 20))
  (cellphone (:type varchar . 20))
  (del (:type char . 1) (:not-null . t))
  (:primary-key . idno)
  ))

as a list. (the actual result is NOT pretty-printed)

For instance, you can use this list to generate some input-form. Once we get into the lisp world, you can try many thins using REPL. That may be fun.

Language features

Integers, reals, and strings can be used as atomic values.

Functions and variables share the same name space. It's a deep binding and dynamic scoping lisp.

` works in macro definitions as well as , and ,@.

Tail-calls are executed by jumps.

form	implementation	explanation
>	C	numberic comparison
>=	C
<	C
<=	C
%	C	arithmetic binary operator
mul2	C
sub2	C
add2	C
div2	C
if	C
not	C
setq	C
quote	C	' can be used instead
_bquote	C
dump	C
gc	C	force garbage collection
cons	C
env	C
car	C
cdr	C
cdr!	C
=	C
eq	C
atom	C
intp	C
nump	C
symbolp	C
symbolp:	C
listp	C
consp	C
null	C
endp	C
and	C
or	C
progn	C
let	C
let*	C
parse	C	invoke your parser
intern	C
cond	C
concatenate	C	string concatination
cons-counter	C
pr	C	print things
prln	C	pr with new-line
len	C	string length
assoc	C
2str	C	making a string from integer or real
gensym	C	generate a new symbol
macroexpand	C	expand macro just once
funcall	C
apply	C
eval	C
range	C	returns a list of numbers between given two integers
foreach	C	(foreach i <list> expr1 expr2 ...)
foreach-t	C	same syntax as foreach
defun	lisp
defmacro	lisp
unless	lisp
fac	lisp
append	lisp
reverse	lisp
length	lisp
nth	lisp
+	lisp	arithmetic operator taking any number of perands
-	lisp
/	lisp
*	lisp
equal	lisp
cat	lisp	string concatination for any number of strings

---

yaccで生成したパーサの意味付けをLispで

yaccで作ったパーサでパース後、意味付けをするのにlispのリストが使えれば便利だと思って作りました. "anoter lisp, again?"と思われた方、すみません.

インタープリタは、吉田裕美さんの「ちょっと変わったLisp入門」をベースにしています. 本人のご許可を頂きました.

https://atmarkit.itmedia.co.jp/ait/articles/0810/31/news148.html

$$にconsセルを代入すれば、結果をリストとして受け取ることができます. ASTがリストになれば、lispでいろいろ触わることができます.

REPLから(parse "input.txt")としてパーサーを呼び出します. ただし、スキャナや文法はそれぞれlex.lとyacc.yにハードコードされているので、 文法を変更した場合は、makeして全体を作り直す必要があります.

例

今はyacc.yにSQLのcreate table文の文法が定義してあります.

k.sqlの内容が以下だとして、

create table tmEmp (
        idno                    decimal(15,0) not null          -- ID
                                default autoincrement,
        code                    varchar(5) not null,            -- コード
        nm                      varchar(40) not null,           -- 名前
        zip                     varchar(10),                    -- 郵便番号
        addr                    varchar(80),                    -- 住所
        phone                   varchar(20),                    -- 電話番号
        cellphone               varchar(20),                    -- 携帯番号
        del                     char(1) not null,               -- 削除FLG
        primary key(idno)
)

lispのREPLで(parse "k.sql")を評価すると、

((tmEmp
  (idno (:type decimal 15 . 0) (:not-null . t) (:autoincrement . t))
  (code (:type varchar . 5) (:not-null . t))
  (nm (:type varchar . 40) (:not-null . t))
  (zip (:type varchar . 10))
  (addr (:type varchar . 80))
  (phone (:type varchar . 20))
  (cellphone (:type varchar . 20))
  (del (:type char . 1) (:not-null . t))
  (:primary-key . idno)
  ))

が返ります. (※実際には、ppされないベタなフォームとして印字されます)

例えば、これを適当に走査して入力画面を生成したりするのに使えるでしょう. 一旦lispの世界に入ってしまえば、REPLからいろいろなことが試せて面白そうです.