.so tmac.ilib
.TH PDCO 2 "The University of Arizona \- 8/16/84"
.SH NAME
pdco \- programmer-defined control operations
.SH DESCRIPTION
These procedures are taken mainly from TR 82-8, which describes
how co-expressions can be used to model the built-in control
structures of Icon and also provide new ones. Some procedures have
been corrected or improved and there are additions.
.SH SYNOPSIS
.nf
.ta 2.0i
\*MAlt\^{e1,\*be2}\fR	models \*Me1 | e2\fR
\*MColseq\^{e1,\*be2, \*(El}\fR	produces results of \*Me1\fR, \*Me2\fR, \*(El alternately
\*MComseq\^{e1,\*be2}\fR	compares result sequences of \*Me1\fR and \*Me2\fR
\*MCond\^{e1,\*be2, \*(El}\fR	generalized Lisp conditional
\*MEvery\^{e1,\*be2}\fR	models \*Mevery e1 do e2\fR
\*MGalt\^{e1,\*be2, \*(El}\fR	generalized alternation: \*Me1 | e2 | \*(El\fR
\*MLcond\^{e1,\*be2, \*(El}\fR	Lisp conditional
\*MLimit\^{e1,\*be2}\fR	models \*Me1 \e e2\fR
\*MRanseq\^{e1,\*be2, \*(El}\fR	produces results of \*Me1\fR, \*Me2\fR, \*(El at random
\*MRepalt\^{e}\fR	models \*M|e\fR
\*MResume\^{e1,\*be2,\*be3}\fR	models \*Mevery e1 \e e2 do e3\fR
\*MSelect\^{e1,\*be2}\fR	produces results from \*Me1\fR by position according to \*Me2\fR
.SH BUGS AND DEFICIENCIES
Because of the handling of the scope of local identifiers in co-expressions,
expressions in programmer-defined control operations cannot communicate
through local identifiers. The results produced by programmer-defined
control operations are always dereferenced. Some constructions, such
as \*Mbreak\fR and \*Mreturn\fR, cannot be used in arguments to programmer-defined
control operations. See TR 82-8 for details of these problems.
.SH REQUIREMENTS
\fIPdco\fR requires the experimental extensions in Version 5.9 of Icon.
.SH SEE ALSO
pdae(2)
.PP
.Pd
.PP
.Ex
.SH AUTHORS
Ralph E. Griswold and Michael Novak