Wildcard targets in a Makefile

The concept is called pattern rules. You can read about it in GNU make manual.

$(GRAPHDIR)/%.png: $(GRAPHDIR)/%.dot
        dot $< -Tpng -o $@

graphs: $(patsubst %,$(GRAPHDIR)/%.png, Complex Simple IFileReader McCabe)\

or just

%.png: %.dot
        dot $< -Tpng -o $@

graphs: $(patsubst %,$(GRAPHDIR)/%.png, Complex Simple IFileReader McCabe)

You can also remove all repetition by extracting one of the patterns into a separate variable PNG_PATTERN like so:

PNG_pattern=$(GRAPHDIR)/%.png

$(PNG_pattern): $(GRAPHDIR)/%.dot
        dot $< -Tpng -o $@

graphs: $(patsubst %,$(PNG_pattern), Complex Simple IFileReader McCabe)