+
+## A second example
+
+I had originally thought that the LR05 style grammar would suit me there
+should never be a sequence of token that means either of two different
+things depending on what comes follows it. Without that ambiguity, the
+extra strength of LALR, or even SLR, would not be needed. However I
+discovered this was too simplistic. There are times when it is quite
+reasonable for the empty string, or maybe a NEWLINE, to have different
+meanings depending on the next token. For this, LR05 is not sufficient,
+so I added full action-table support.
+
+This example tests the selection of REDUCE actions based on the
+look-ahead symbol, using a trivial grammar where the empty string can
+reasonably mean different things depending on what it precedes.
+
+
+####### File: parsergen.mk
+ demos :: do_lalr_demo
+ lalr_demo.c lalr_demo.h : parsergen parsergen.mdc
+ ./parsergen --LALR --tag demo -o lalr_demo parsergen.mdc
+ lalr_demo: lalr_demo.o libparser.o libscanner.o libmdcode.o
+ $(CC) -o lalr_demo lalr_demo.c libparser.o libscanner.o libmdcode.o -licuuc
+ do_lalr_demo: lalr_demo
+ NOTRACE=1 ./lalr_demo
+ @echo 'Should produce "start of line, empty sign, empty sigl"'
+
+####### demo: grammar
+
+ $TERM $ @ + -
+ line -> ${ printf("start of line"); }$
+ | line term
+ term -> sigl IDENTIFIER
+ | sign NUMBER
+ sigl -> $
+ | @
+ | ${ printf(", empty sigl"); }$
+ sign -> +
+ | -
+ | ${ printf(", empty sign"); }$
+
+####### demo: header
+
+ //
+
+####### demo: code
+
+ #include <stdlib.h>
+ #include <stdio.h>
+ #include "mdcode.h"
+ #include "scanner.h"
+ #include "parser.h"
+ #include "lalr_demo.h"
+ int main(int argc, char *argv[])
+ {
+ char test[] = "````\n$a -1 5 b\n";
+ struct section *table = code_extract(test, test+sizeof(test)-1, NULL);
+ struct token_config config = {
+ .ignored = (1 << TK_line_comment)
+ | (1 << TK_newline)
+ | (1 << TK_in)
+ | (1 << TK_out),
+ .number_chars = "",
+ .word_start = "",
+ .word_cont = "",
+ };
+ parse_lalr_demo(table->code, &config, getenv("NOTRACE") ? NULL : stderr);
+ printf("\n");
+ exit(0);
+ }
code / ocean / blobdiff