first commit

perl/Examples/Chap4/Iterator_Utils.pm

@@ -0,0 +1,105 @@
+
+
+###
+### Iterator_Utils.pm
+###
+
+## Chapter 4 section 2.1
+
+package Iterator_Utils;
+use base Exporter;
+@EXPORT_OK = qw(NEXTVAL Iterator 
+                append imap igrep
+                iterate_function filehandle_iterator list_iterator);
+%EXPORT_TAGS = ('all' => \@EXPORT_OK);
+
+sub NEXTVAL { $_[0]->() }
+
+
+## Chapter 4 section 2.1.1
+
+sub Iterator (&) { return $_[0] }
+
+
+## Chapter 4 section 3.1
+
+sub iterate_function {
+  my $n = 0;
+  my $f = shift;
+  return Iterator {  
+    return $f->($n++);
+  };
+}
+
+
+## Chapter 4 section 3.3
+
+sub filehandle_iterator {
+  my $fh = shift;
+  return Iterator { <$fh> };
+}
+1;
+
+
+## Chapter 4 section 4.1
+
+sub imap (&$) {
+  my ($transform, $it) = @_;
+  return Iterator {
+    local $_ = NEXTVAL($it);
+    return unless defined $_;
+    return $transform->();
+  }
+}
+
+
+## Chapter 4 section 4.2
+
+sub igrep (&$) {
+  my ($is_interesting, $it) = @_;
+  return Iterator {
+    local $_;
+    while (defined ($_ = NEXTVAL($it))) {
+      return $_ if $is_interesting->();
+    }
+    return;
+  }
+}
+
+
+## Chapter 4 section 4.3
+
+sub list_iterator {
+  my @items = @_;
+  return Iterator {
+    return shift @items;
+  };
+}
+
+
+## Chapter 4 section 4.4
+
+sub append {
+  my @its = @_;
+  return Iterator {
+    while (@its) {
+      my $val = NEXTVAL($its[0]);
+      return $val if defined $val;
+      shift @its;  # Discard exhausted iterator
+    }
+    return;
+  };
+}
+
+
+## Chapter 4 section 7.2
+
+sub igrep_l (&$) {
+  my ($is_interesting, $it) = @_;
+  return Iterator {
+    while (my @vals = NEXTVAL($it)) {
+      return @vals if $is_interesting->(@vals);
+    }
+    return;
+  }
+}