diff options
Diffstat (limited to 'cppawk-cons.1')
| -rw-r--r-- | cppawk-cons.1 | 95 |
1 files changed, 83 insertions, 12 deletions
diff --git a/cppawk-cons.1 b/cppawk-cons.1 index 200876b..47bb0da 100644 --- a/cppawk-cons.1 +++ b/cppawk-cons.1 @@ -69,6 +69,7 @@ cons \- Lisp-like data representation and control flow macros sexp(x) // convert Lisp value to S-expression string equal(x, y) // test whether two Lisp values are equal + equalize(x) // convert object to canonical representation list(...) // return argument values as a Lisp list append(...) // append list arguments; last may be atom @@ -888,12 +889,13 @@ function favors the last of these. (nil . 1) .ft R -.SS Function \fIequal\fP +.SS Functions \fIequal\fP and \fIequalize\fP .bk .B Syntax: .ft B equal(x, y) + equalize(x) .ft R .B Description @@ -932,9 +934,9 @@ If .I x and .I y -are both numeric, then they are compared numerically, even if -they are character strings. While this may seem to be the same as Awk equality, -it is not the case. This rule is applied regardless of the origin of +are both numbers, then they are compared numerically, While this may seem to be +the same as Awk equality, that is not the case. This rule is applied regardless +of the origin of .I x and .IR y . @@ -964,22 +966,26 @@ will print 1 when a record with the fields .B 1 and .B 1.0 -is processed. This is because at input time, Awk classifies such -inputs as being numeric strings, attaching that to their type -information, and two numeric strings are compared as numbers. -Loosely speaking, the +is processed. This is because Awk classifies certain inputs, such as fields +delmited during input scanning, as being numeric strings if they look like +numbers. This numeric string status is attached to their type information, and +two numeric strings are compared as numbers. Yet, strings character-for-character +identical to these which are produced via string manipulation are not treated +as numeric. Loosely speaking, the .B equal -function compares two strings as numbers if they would be numeric +function compares two (unboxed) strings as numbers if they would be numeric strings if they were input as Awk fields. .IP 2. -A box string is +A boxed string is .B equal -to an unboxed string of the same content, even though their Awk -representation is different. In implementation terms: +to an unboxed string of the same content, but only if the unboxed +string isn't numeric. A numeric unboxed string is considered a number, +and thus not equal to any boxed string. .ft B equal("Tabc", "abc") => 1 + equal("T123", "123") => 0 .ft R .IP 3. @@ -1003,6 +1009,71 @@ to .BI cdr( y ) .PP +The +.B equalize +function is semantically related to +.BR equal . +It computes and returns an object similar to its argument object. +If two objects +.I x +and +.I y +are considered to be the same by the +.B equal +function, then the expressions +.BI equalize( x ) +and +.BI equalize( y ) +each return the same string. + +That is to say, the following relationship holds between +.B equalize +and +.BR equal : + +.ft B + equal(\fIx\fP, \fIy\fP) == (equalize(\fIx\fP) == equalize(\fIy\fP)) +.ft R + +Comparing two objects for equality using +.B equal +is the same as converting them to a canonical representation with +.B equalize +and then comparing that representation using the +.B == +operator. + +The +.b equalize +function is useful for two reasons. Firstly, comparing objects with +.B == +is much cheaper than +.BR equal ; +therefore, an application which performs a lot of comparisons +may be made more efficient if it equalizes the objects and then +uses the +.B == +operator instead of +.BR equal . + +Secondly, when equalized objects are used as keys for an Awk associative +array, then, effectively, that array becomes based on +.BR equal +equality. That is to say, for instance, if the the objects +.B "cons("1.0", "2.0")" +and +.B "cons(1, 2)" +are used directly as associative array keys, they are different keys because +their string representation is different. Yet, those two objects are +.BN equal . +Suppose that in some application there exists the requirement that +.B equal +objects must be be considered to be the same array key. This requirement +can be satisfied by passing all keys through the +.B equalize +function, and using the equalized images of the keys for the +array operations. + .SH "SEE ALSO" cppawk(1) |