branch: externals/parser-generator
commit b73c4ed6c88740f8e422ade0358dc4cd2cd78c6e
Author: Christian Johansson <[email protected]>
Commit: Christian Johansson <[email protected]>
Made e-symbol customizable
---
README.md | 2 +-
parser.el | 36 ++++++++++++++++++++----------------
2 files changed, 21 insertions(+), 17 deletions(-)
diff --git a/README.md b/README.md
index 8c514f2..aa3667c 100644
--- a/README.md
+++ b/README.md
@@ -49,7 +49,7 @@ Grammar consists of `N`, `T`, `P` and `S`, where `N` is
non-terminals, `T` is te
### e
-The symbol `'e` is hard-coded to be the empty symbol. The symbol is allowed in
some grammars and not in others.
+The symbol defined in variable `parser--e-identifier`, with default-value:
'e`, symbolizes the e symbol. The symbol is allowed in some grammars and not in
others.
### Non-terminals
diff --git a/parser.el b/parser.el
index a2f2b32..efa4dfe 100644
--- a/parser.el
+++ b/parser.el
@@ -14,29 +14,33 @@
nil
"Whether to print debug messages or not.")
-(defvar parser--table-non-terminal-p
+(defvar parser--e-identifier
+ 'e
+ "The identifier used for e-symbol. Default value 'e.")
+
+(defvar parser--grammar
nil
- "Hash-table of terminals for quick checking.")
+ "Current grammar used in parser.")
-(defvar parser--table-productions
+(defvar parser--f-sets
nil
- "Hash-table of productions for quick retrieving.")
+ "Generated F-sets for grammar.")
-(defvar parser--table-terminal-p
+(defvar parser--look-ahead-number
nil
- "Hash-table of non-terminals for quick checking.")
+ "Current look-ahead number used.")
-(defvar parser--grammar
+(defvar parser--table-non-terminal-p
nil
- "Current grammar used in parser.")
+ "Hash-table of terminals for quick checking.")
-(defvar parser--look-ahead-number
+(defvar parser--table-productions
nil
- "Current look-ahead number used.")
+ "Hash-table of productions for quick retrieving.")
-(defvar parser--f-sets
+(defvar parser--table-terminal-p
nil
- "Generated F-sets for grammar.")
+ "Hash-table of non-terminals for quick checking.")
;; Macros
@@ -167,7 +171,7 @@
(defun parser--valid-e-p (symbol)
"Return whether SYMBOL is the e identifier or not."
- (eq symbol 'e))
+ (eq symbol parser--e-identifier))
(defun parser--valid-grammar-p (G)
"Return if grammar G is valid or not. Grammar should contain list with 4
elements: non-terminals (N), terminals (T), productions (P), start (S) where N,
T and P are lists containing symbols and/or strings and S is a symbol or
string."
@@ -649,7 +653,7 @@
(let ((S)
(marked-sets (make-hash-table :test 'equal))
(symbols (append (parser--get-grammar-non-terminals)
(parser--get-grammar-terminals))))
- (let ((e-set (parser--lr-items-for-prefix 'e)))
+ (let ((e-set (parser--lr-items-for-prefix parser--e-identifier)))
;; TODO (1) Place V(e) in S. The set V(e) is initially unmarked.
)
(let ((found-unmarked t))
@@ -731,7 +735,7 @@
;; Set follow to nil if it's the e-identifier
(when (and
(= (length sub-rhs) 1)
- (eq (car sub-rhs) 'e))
+ (parser--valid-e-p (car sub-rhs)))
(setq sub-rhs nil))
(parser--debug
@@ -756,7 +760,7 @@
;; 2 Suppose that we have constructed V(X1,X2,...,Xi-1) we construct
V(X1,X2,...,Xi) as follows:
(unless (and
(= (length γ) 1)
- (eq (car γ) 'e))
+ (parser--valid-e-p (car γ)))
(let ((prefix-acc)
(prefix-previous (gethash '(e) lr-items)))
(dolist (prefix γ)
