reduce-historical/psl-1983/help/mini.hlp

The MINI translator writing system 
---------------------------------- 

MINI processes a BNF-like form into a set of LISP functions, one for each
production, operating on a stack and token-stream.  They call each other,
and a set of support routines and built-in recognizers.   MINI uses a stack;
the user can access sub-trees on the stack, replacing them by other trees
built from these sub-trees.   Primitive recognizers their recognized token
on this stack.

==================== Load mini by doing LOAD MINI; in RLISP.

==================== The translator is defined by MINI 'rootname;

MINI 'FOO;
  FOO: ID '!- ID +(SUB #2 #1) .(PRINT #1) ;
FIN

defines a complete one rule translator, which recognizes two identifiers
separated by a minus sign (each ID pushes the recognized identifier onto
the stack).  The +() expression replaces the top 2 elements on the stack
(#2 pops the first ID pushed onto the stack, while #1 pops the other) with
a LISP statement.  The .() expression POPs and prints it.

	See also <griss.mini> for demo0.MIN to demo3.MIN

============Run the Grammer by calling INVOKE 'FOO; % i.e. the rootname

============Built In Recognizers: ID, NUM, STR, ANYTOKEN

============Brief list of the operators
'	Used to designate a terminal symbol (i.e. 'WHILE, 'DO, '!=)
Identifier	Specifies a nonterminal
( )	Used for grouping (i.e. (FOO BAR) requires rule FOO to parse
	followed immediately by BAR)
< >	Optional parse, if it fails then continue (i.e. <FOO> tries
	to parse FOO)
/	Optional rules (i.e. FOO / BAR allows either FOO or BAR to
	parse, with FOO tested first)

STMT[ANYTOKEN]*	Parse any number of STMT separated by ANYTOKEN,
	create a list and push onto the stack (i.e. ID[,]* will parse a
	number of IDentifiers separated by commas, like in an argument
	list)
##n	Reference the nth stack location (n must be an integer)
#n	Pop the nth stack location (n must be an integer)
+(STMT)	Push the unevaluated (STMT) onto the stack 
.(SEXPR)	Evaluate the SEXPR and ignore the result
=(SEXPR)	Evaluate the SEXPR and test if result non-NIL
+.(SEXPR)	Evaluate the SEXPR and push the result on the stack
@ANYTOKEN	Specifies a statement terminator, used in the error
		recovery mechanism to search for when an error occurs;
	        like 'ANYTOKEN, but causes NEXT!-TOK to not scan ahead
		so .(NEXT!-TOK) may be needed
@@ANYTOKEN	Specifies a grammer terminator, used in the error
		recovery mechanism to search for when an error occurs;
	        like @ANYTOKEN; fatal exit in Error Recovery
$integer        Generates a unique label

================== Pattern MATCHER

In addition to BNF -like rules that define procedures on 0 arguments (which
scan tokens by calls on NEXT!-TOK() and operate on the stack, MINI also
includes a simple TREE pattern matcher and syntax to define
PatternProcedures that accept and return a single argument, trying a series
of patterns until one succeeds.

E.g.        template    ->  replacement
   
PATTERN = (PLUS2 &1 0) -> 0,
          (PLUS2 &1 &1) -> (LIST 'TIMES2 2 &1),
          &1            -> &1;

defines a pattern with 3 rules.  &n is used to indicate a matched sub-tree
in both the template and replacement.  A repeated &n as in the second rule
requires EQUAL sub-trees.