Confusing error message with redundant generic names

[phorward]

This script

Assignment : @<Expression, Assignment: Assignment, ext: void> {
    Ident _ '=' _ Expect<Assignment>  ast("assign" + ext)
    Expression  ast("value")
}

ast_print(Assignment<Int>)

generates the error messages

'Assignment' requires assignment of generic argument 'Expression'
'Assignment' requires assignment of generic argument 'Expression'

---

When, according to the error message hint, the script is changed into this version:

Assignment : @<Expression, Assignment: Assignment, ext: void> {
    Ident _ '=' _ Expect<Assignment<Int>>  ast("assign" + ext)
    Expression  ast("value")
}

ast_print(Assignment<Int>)

the error messages gets more confusing:

Line 2, column 26: Use of undefined name 'Assignment<Int>'