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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: |