Implementation of TIP #405.

2 files changed, 112 insertions, 2 deletions

diff --git a/doc/dict.n b/doc/dict.n
index 361a112..3bd5530 100644
--- a/doc/dict.n
+++ b/doc/dict.n
@@ -147,6 +147,31 @@ keys are treated as if they map to an empty list, and it is legal for
 there to be no items to append to the list. It is an error for the
 value that the key maps to to not be representable as a list.
 .TP
+\fBdict map \fR{\fIkeyVar valueVar\fR} \fIdictionaryValue body\fR
+.
+This command applies a transformation to each element of a dictionary,
+returning a new dictionary. It takes three arguments: the first is a
+two-element list of variable names (for the key and value respectively of each
+mapping in the dictionary), the second the dictionary value to iterate across,
+and the third a script to be evaluated for each mapping with the key and value
+variables set appropriately (in the manner of \fBlmap\fR). In an iteration
+where the evaluated script completes normally (\fBTCL_OK\fR, as opposed to an
+\fBerror\fR, etc.) the result of the script is put into an accumulator
+dictionary using the key that is the current contents of the \fIkeyVar\fR
+variable at that point. The result of the \fBdict map\fB command is the
+accumulator dictionary after all keys have been iterated over.
+.RS
+.PP
+If the evaluation of the body for any particular step generates a \fBbreak\fR,
+no further pairs from the dictionary will be iterated over and the \fBdict
+map\fR command will terminate successfully immediately. If the evaluation of
+the body for a particular step generates a \fBcontinue\fR result, the current
+iteration is aborted and the accumulator dictionary is not modified. The order
+of iteration is the natural order of the dictionary (typically the order in
+which the keys were added to the dictionary; the order is the same as that
+used in \fBdict for\fR).
+.RE
+.TP
 \fBdict merge \fR?\fIdictionaryValue ...\fR?
 .
 Return a dictionary that contains the contents of each of the
@@ -408,9 +433,9 @@ puts $foo
 #    prints: \fIa b foo {a b} bar 2 baz 3\fR
 .CE
 .SH "SEE ALSO"
-append(n), array(n), foreach(n), incr(n), list(n), lappend(n), set(n)
+append(n), array(n), foreach(n), mapeach(n), incr(n), list(n), lappend(n), set(n)
 .SH KEYWORDS
-dictionary, create, update, lookup, iterate, filter
+dictionary, create, update, lookup, iterate, filter, map
 '\" Local Variables:
 '\" mode: nroff
 '\" End:
diff --git a/doc/lmap.n b/doc/lmap.n
new file mode 100644
index 0000000..880b05a
--- /dev/null
+++ b/doc/lmap.n
@@ -0,0 +1,85 @@
+'\"
+'\" Copyright (c) 2012 Trevor Davel
+'\"
+'\" See the file "license.terms" for information on usage and redistribution
+'\" of this file, and for a DISCLAIMER OF ALL WARRANTIES.
+'\" 
+.so man.macros
+.TH lmap n "" Tcl "Tcl Built-In Commands"
+.BS
+'\" Note:  do not modify the .SH NAME line immediately below!
+.SH NAME
+lmap \- Iterate over all elements in one or more lists and collect results
+.SH SYNOPSIS
+\fBlmap \fIvarname list body\fR
+.br
+\fBlmap \fIvarlist1 list1\fR ?\fIvarlist2 list2 ...\fR? \fIbody\fR
+.BE
+.SH DESCRIPTION
+.PP
+The \fBlmap\fR command implements a loop where the loop variable(s) take on
+values from one or more lists, and the loop returns a list of results
+collected from each iteration.
+.PP
+In the simplest case there is one loop variable, \fIvarname\fR, and one list,
+\fIlist\fR, that is a list of values to assign to \fIvarname\fR. The
+\fIbody\fR argument is a Tcl script. For each element of \fIlist\fR (in order
+from first to last), \fBlmap\fR assigns the contents of the element to
+\fIvarname\fR as if the \fBlindex\fR command had been used to extract the
+element, then calls the Tcl interpreter to execute \fIbody\fR. If execution of
+the body completes normally then the result of the body is appended to an
+accumulator list. \fBlmap\fR returns the accumulator list.
+.PP
+In the general case there can be more than one value list (e.g., \fIlist1\fR
+and \fIlist2\fR), and each value list can be associated with a list of loop
+variables (e.g., \fIvarlist1\fR and \fIvarlist2\fR). During each iteration of
+the loop the variables of each \fIvarlist\fR are assigned consecutive values
+from the corresponding \fIlist\fR. Values in each \fIlist\fR are used in order
+from first to last, and each value is used exactly once. The total number of
+loop iterations is large enough to use up all the values from all the value
+lists. If a value list does not contain enough elements for each of its loop
+variables in each iteration, empty values are used for the missing elements.
+.PP
+The \fBbreak\fR and \fBcontinue\fR statements may be invoked inside
+\fIbody\fR, with the same effect as in the \fBfor\fR and \fBforeach\fR
+commands. In these cases the body does not complete normally and the result is
+not appended to the accumulator list.
+.SH EXAMPLES
+.PP
+Zip lists together:
+.PP
+.CS
+set list1 {a b c d}
+set list2 {1 2 3 4}
+set zipped [\fBlmap\fR a $list1 b $list2 {list $a $b}] 
+# The value of zipped is "{a 1} {b 2} {c 3} {d 4}"
+.CE
+.PP
+Filter a list to remove odd values:
+.PP
+.CS
+set values {1 2 3 4 5 6 7 8}
+proc isEven {n} {expr {($n % 2) == 0}}
+set goodOnes [\fBlmap\fR x $values {expr {
+    [isEven $x] ? $x : [continue]
+}}]
+# The value of goodOnes is "2 4 6 8"
+.CE
+.PP
+Take a prefix from a list based on the contents of the list:
+.PP
+.CS
+set values {8 7 6 5 4 3 2 1}
+proc isGood {counter} {expr {$n > 3}}
+set prefix [\fBlmap\fR x $values {expr {
+    [isGood $x] ? $x : [break]
+}}]
+# The value of prefix is "8 7 6 5 4"
+.CE
+.SH "SEE ALSO"
+break(n), continue(n), for(n), foreach(n), while(n)
+.SH KEYWORDS
+foreach, iteration, list, loop, map
+'\" Local Variables:
+'\" mode: nroff
+'\" End: