From ecbc58fb917c292f05bed401afe7be0a80971d80 Mon Sep 17 00:00:00 2001
From: Robin Haberkorn <robin.haberkorn@googlemail.com>
Date: Wed, 23 Sep 2015 17:53:39 +0200
Subject: different operators can have the same precedence now

 * SciTECO now has the same operator precedence table as C.
 * It is numerically important whether different operators
   have the same precedence. E.g. "5*2/4" used to be evaluated
   by SciTECO as "5*(2/4)" since division had a higher precedence
   than multiplication. Within in real (!) numbers this would
   be the expected evaluation order.
   Users of other programming languages however would expect
   the expression to be evaluated as "(5*2)/4" which makes
   a numerical difference when working with integers.
 * Operator precedence has been implemented by encoding it
   into the enumeration values used to represent different
   operators.
   Calculating the precedence of a given operator can then
   be done very efficiently and elegantly (in our case using
   a plain right shift operation).
 * documentation updated. We use a precedence table now.
---
 doc/sciteco.7.template | 62 +++++++++++++++++++++++++++-----------------------
 1 file changed, 34 insertions(+), 28 deletions(-)

(limited to 'doc/sciteco.7.template')

diff --git a/doc/sciteco.7.template b/doc/sciteco.7.template
index 9c6180c..30d6c76 100644
--- a/doc/sciteco.7.template
+++ b/doc/sciteco.7.template
@@ -726,40 +726,55 @@ command.
 .SS Operators
 .
 The following binary operators are supported with descending
+precedence, whereas borders separate operators of the \fIsame\fP
 precedence:
-.TP 2
-.IB base " ^* " power
+.TS
+expand,box,tab(;);
+L LX.
+\fIbase\fB ^* \fIpower\fR;T{
 Raise \fIbase\fP to \fIpower\fP.
-.TP
-.IB a " ^/ " b
+T}
+=
+\fIa\fB ^/ \fIb\fR;T{
 Remainder of \fIa\fP divided by \fIb\fP.
 It is actually a modulo operation conforming to the
 host C compiler's modulo semantics.
-.TP
-.IB a " / " b
+T}
+\fIa\fB / \fIb\fR;T{
 Divide \fIa\fP by \fIb\fP.
 Naturally it is a division without remainder.
-.TP
-.IB a " * " b
+T}
+\fIa\fB * \fIb\fP;T{
 Multiply \fIa\fP by \fIb\fP.
-.TP
-.IB a " - " b
+T}
+=
+\fIa\fB - \fIb\fP;T{
 Subtract \fIb\fP from \fIa\fP.
-.TP
-.IB a " + " b
+T}
+\fIa\fB + \fIb\fP;T{
 Add \fIb\fP to \fIa\fP.
-.TP
-.IB a " & " b
+T}
+=
+\fIa\fB & \fIb\fP;T{
 Binary AND.
-.TP
-.IB a " ^# " b
+T}
+=
+\fIa\fB ^# \fIb\fP;T{
 Binary exclusive OR (XOR).
-.TP
-.IB a " # " b
+T}
+=
+\fIa\fB # \fIb\fP;T{
 Binary OR.
+T}
+.TE
 .LP
+All binary operators are \fIleft-associative\fP, ie. associate
+from left to right, in \*(ST.
 Round brackets may be used for grouping expressions to override
-operator precedence.
+operator precedence and associativity.
+For instance, since \(lq\fB^/\fP\(rq, \(lq\fB/\fP\(rq and \(lq\fB*\fP\(rq
+all have the same precedence, the expression \(lq1 ^/ 2 / 3 * 4\(rq is
+equivalent to \(lq(((1 ^/ 2) / 3) * 4)\(rq.
 The opening bracket also represents an argument barrier, ie. the first
 command after the opening bracket does not see and cannot pop any
 arguments from the stack.
@@ -774,15 +789,6 @@ mandatory in classic TECO, like in \(lq.ZD\(rq.
 I recommend to use it as much as possible in code where clarity
 matters.
 .LP
-Note that \*(ST assigns an unique precedence to each operator
-instead of having several operators (like addition and subtraction)
-share the same precedence and evaluate them according to their
-associativity.
-Still the precedence rules should ensure that expressions are
-evaluated similarily to other programming languages.
-When the same operator is used repeatedly, expressions are always
-evaluated with left-to-right associativity.
-For instance, \(lq2^*3^*4\(rq is evaluated like \(lq(2^*3)^*4\(rq.
 The arithmetic evaluation order established by the operator precedence
 or braces must not be confused with the execution order of \*(ST commands
 which is always strictly from left to right (unless flow control
-- 
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