From dded89e4e810f13fdf521d6ec8a90ca06ea21675 Mon Sep 17 00:00:00 2001
From: Ludovic Court`es
Date: Tue, 28 Nov 2006 14:40:32 +0000
Subject: eq: Properly handle operator precedence.

* src/guile/skribilo/package/eq.scm (%operator-precedence): Fixed
  according to Wikipedia.
  (simple-markup-writer): Honor operator precedence.

* src/guile/skribilo/package/eq/lout.scm (simple-lout-markup-writer):
  Likewise.

git-archimport-id: lcourtes@laas.fr--2005-libre/skribilo--devo--1.2--patch-83
---
 src/guile/skribilo/package/eq.scm      | 39 +++++++++++++++++++++-------------
 src/guile/skribilo/package/eq/lout.scm | 28 ++++++++++++------------
 2 files changed, 38 insertions(+), 29 deletions(-)

diff --git a/src/guile/skribilo/package/eq.scm b/src/guile/skribilo/package/eq.scm
index c45f698..a3eb99c 100644
--- a/src/guile/skribilo/package/eq.scm
+++ b/src/guile/skribilo/package/eq.scm
@@ -116,18 +116,27 @@ a symbol representing the mathematical operator denoted by @var{m} (e.g.,
 ;;;
 
 (define %operator-precedence
-  ;; FIXME: This needs to be augmented.
-  '((+ . 1)
-    (- . 1)
-    (* . 2)
-    (/ . 2)
-    (sum . 3)
+  ;; Taken from http://en.wikipedia.org/wiki/Order_of_operations .
+  '((expt . 2)
+    (sqrt . 2)
+
+    (* . 3)
+    (/ . 3)
     (product . 3)
-    (= . 0)
-    (< . 0)
-    (> . 0)
-    (<= . 0)
-    (>= . 0)))
+
+    (+ . 4)
+    (- . 4)
+    (sum . 4)
+
+    (< . 6)
+    (> . 6)
+    (<= . 6)
+    (>= . 6)
+
+    (= . 7)
+    (!= . 7)
+    (~= . 7)))
+
 
 (define-public (operator-precedence op)
   (let ((p (assq op %operator-precedence)))
@@ -329,10 +338,10 @@ a symbol representing the mathematical operator denoted by @var{m} (e.g.,
 			      (nested-eq? (equation-markup? o))
 			      (need-paren?
 			       (and nested-eq?
-; 				    (< (operator-precedence
-; 					(equation-markup-name->operator
-; 					 (markup-markup o)))
-; 				       ,precedence)
+ 				    (>= (operator-precedence
+                                         (equation-markup-name->operator
+                                          (markup-markup o)))
+                                        ,precedence)
 				    )
 			       ))
 
diff --git a/src/guile/skribilo/package/eq/lout.scm b/src/guile/skribilo/package/eq/lout.scm
index 563fdbf..9cd594b 100644
--- a/src/guile/skribilo/package/eq/lout.scm
+++ b/src/guile/skribilo/package/eq/lout.scm
@@ -85,8 +85,12 @@
 
 	 ;; Note: We could use `pmatrix' here but it precludes line-breaking
 	 ;; within equations.
-	 (open-par `(if need-paren? "{ @VScale ( }" ""))
-	 (close-par `(if need-paren? "{ @VScale ) }" "")))
+	 (open-par (if parentheses?
+                       `(if need-paren? "{ @VScale ( }" "")
+                       ""))
+	 (close-par (if parentheses?
+                        `(if need-paren? "{ @VScale ) }" "")
+                        "")))
 
     `(markup-writer ',(symbol-append 'eq: sym)
 		    (find-engine 'lout)
@@ -102,25 +106,21 @@
                                              (eq-op? (equation-markup? op))
                                              (need-paren?
                                               (and eq-op?
-                                                   (< (operator-precedence
-                                                       (equation-markup-name->operator
-                                                        (markup-markup op)))
-                                                      ,precedence)))
+                                                   (>= (operator-precedence
+                                                        (equation-markup-name->operator
+                                                         (markup-markup op)))
+                                                       ,precedence)))
                                              (column (port-column
                                                       (current-output-port))))
 
                                         ;; Work around Lout's limitations...
                                         (if (> column 1000) (display "\n"))
 
-                                        (display (string-append " { "
-                                                                ,(if parentheses?
-                                                                     open-par
-                                                                     "")))
+                                        (display
+                                         (string-append " { " ,open-par))
                                         (output op engine)
-                                        (display (string-append ,(if parentheses?
-                                                                     close-par
-                                                                     "")
-                                                                " }"))
+                                        (display
+                                         (string-append ,close-par " }"))
                                         (if (pair? (cdr operands))
                                             (display (string-append " "
                                                                     lout-name
-- 
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