Tcl Source Code

\fBTcl\fR.
.PP
Below are some examples of simple expressions where the value of \fBa\fR is 3
and the value of \fBb\fR is 6.  The command on the left side of each line
produces the value on the right side.
.PP
.CS
.ta 8c
\fBexpr\fR 3.1 + $a	\fI6.1\fR
\fBexpr\fR 2 + "$a.$b"	\fI5.6\fR
\fBexpr\fR 4*[llength "6 2"]	\fI8\fR
\fBexpr\fR {{word one} < "word $a"}	\fI0\fR
.CE
.SS OPERATORS
.PP
................................................................................
Bit-wise OR.  Valid for integer operands.
.TP 20
\fB&&\fR
.
Logical AND.  If both operands are true, the result is 1, or 0 otherwise.
This operator evaluates lazily; it only evaluates its second operand if it
must in order to determine its result.


.TP 20
\fB||\fR
.
Logical OR.  If both operands are false, the result is 0, or 1 otherwise.
This operator evaluates lazily; it only evaluates its second operand if it
must in order to determine its result.
.TP 20
................................................................................
This operator evaluates lazily; it evaluates only one of \fIy\fR or \fIz\fR.
.PP
The exponentiation operator promotes types in the same way that the multiply
and divide operators do, and the result is is the same as the result of
\fBpow\fR.
Exponentiation groups right-to-left within a precedence level. Other binary
operators group left-to-right.  For example, the value of

.PP
.CS
\fBexpr\fR {4*2 < 7}
.CE
.PP
is 0, while the value of
.PP
................................................................................
substitutions on, enclosing an expression in braces or otherwise quoting it
so that it's a static value allows the Tcl compiler to generate bytecode for
the expression, resulting in better speed and smaller storage requirements.
This also avoids issues that can arise if Tcl is allowed to perform
substitution on the value before \fBexpr\fR is called.
.PP
In the following example, the value of the expression is 11 because the Tcl parser first
substitutes \fB$b\fR and \fBexpr\fR then substitutes \fB$a\fR.  Enclosing the



expression in braces would result in a syntax error.

.PP
.CS
set a 3
set b {$a + 2}
\fBexpr\fR $b*4
.CE
.PP

\fBTcl\fR.
.PP
Below are some examples of simple expressions where the value of \fBa\fR is 3
and the value of \fBb\fR is 6.  The command on the left side of each line
produces the value on the right side.
.PP
.CS
.ta 9c
\fBexpr\fR 3.1 + $a	\fI6.1\fR
\fBexpr\fR 2 + "$a.$b"	\fI5.6\fR
\fBexpr\fR 4*[llength "6 2"]	\fI8\fR
\fBexpr\fR {{word one} < "word $a"}	\fI0\fR
.CE
.SS OPERATORS
.PP
................................................................................
Bit-wise OR.  Valid for integer operands.
.TP 20
\fB&&\fR
.
Logical AND.  If both operands are true, the result is 1, or 0 otherwise.
This operator evaluates lazily; it only evaluates its second operand if it
must in order to determine its result.
This operator evaluates lazily; it only evaluates its second operand if it
must in order to determine its result.
.TP 20
\fB||\fR
.
Logical OR.  If both operands are false, the result is 0, or 1 otherwise.
This operator evaluates lazily; it only evaluates its second operand if it
must in order to determine its result.
.TP 20
................................................................................
This operator evaluates lazily; it evaluates only one of \fIy\fR or \fIz\fR.
.PP
The exponentiation operator promotes types in the same way that the multiply
and divide operators do, and the result is is the same as the result of
\fBpow\fR.
Exponentiation groups right-to-left within a precedence level. Other binary
operators group left-to-right.  For example, the value of
.PP
.PP
.CS
\fBexpr\fR {4*2 < 7}
.CE
.PP
is 0, while the value of
.PP
................................................................................
substitutions on, enclosing an expression in braces or otherwise quoting it
so that it's a static value allows the Tcl compiler to generate bytecode for
the expression, resulting in better speed and smaller storage requirements.
This also avoids issues that can arise if Tcl is allowed to perform
substitution on the value before \fBexpr\fR is called.
.PP
In the following example, the value of the expression is 11 because the Tcl parser first
substitutes \fB$b\fR and \fBexpr\fR then substitutes \fB$a\fR as part
of evaluating the expression
.QW "$a + 2*4" .
Enclosing the
expression in braces would result in a syntax error as \fB$b\fR does
not evaluate to a numeric value.
.PP
.CS
set a 3
set b {$a + 2}
\fBexpr\fR $b*4
.CE
.PP