schema: connect validation, Compile() now works.

More rules are still to come.

schema/compiler.go

@@ -66,8 +66,21 @@ func (c *Compiler) Init() {
 	}
 }
 
-func (c *Compiler) Compile() (*TypeSystem, error) {
-	panic("TODO")
+func (c *Compiler) Compile() (*TypeSystem, []error) {
+	var errs []error
+	for _, typ := range c.ts.list {
+		validate(c.ts, typ, &errs)
+	}
+	// TODO sort ts.anonTypes
+	for _, typ := range c.ts.anonTypes {
+		validate(c.ts, typ, &errs)
+	}
+	if errs != nil {
+		return nil, errs
+	}
+	result := c.ts
+	c.ts = nil // result shall now be immutable
+	return result, nil
 }
 
 func (c *Compiler) MustCompile() *TypeSystem {

schema/dmt/compile.go

@@ -10,7 +10,7 @@ import (
 //  and so we've just chained it all together with switch statements;
 //   creating a separate interface per result type seems just not super relevant.
 
-func (schdmt Schema) Compile() (*schema.TypeSystem, error) {
+func (schdmt Schema) Compile() (*schema.TypeSystem, []error) {
 	c := &schema.Compiler{}
 	typesdmt := schdmt.FieldTypes()
 	for itr := typesdmt.Iterator(); !itr.Done(); {