loader: switch to custom program loader

loader/errors.go

@@ -0,0 +1,27 @@
+package loader
+
+// Errors contains a list of parser errors or a list of typechecker errors for
+// the given package.
+type Errors struct {
+	Pkg  *Package
+	Errs []error
+}
+
+func (e Errors) Error() string {
+	return "could not compile: " + e.Errs[0].Error()
+}
+
+// ImportCycleErrors is returned when encountering an import cycle. The list of
+// packages is a list from the root package to the leaf package that imports one
+// of the packages in the list.
+type ImportCycleError struct {
+	Packages []string
+}
+
+func (e *ImportCycleError) Error() string {
+	msg := "import cycle: " + e.Packages[0]
+	for _, path := range e.Packages[1:] {
+		msg += " → " + path
+	}
+	return msg
+}