The louder failure had the quieter answer. A generated reader accumulates
errors on the cursor — which is what lets it be a straight line of
assignments — and the cursor is made and dropped inside the entry point, so a
stray brace in a file read at run time handed the program a zeroed struct and
said nothing at all. That is the one thing the rest of vendor:edn refuses to
do: read-file answers an Option precisely so a malformed document is
distinguishable from one that is literally nil, and the hand-written reader in
test/programs/edn.flan tests ok? and prints the reason. ReadFailed is the
derived reader being as honest, in both packages, and it sits beside
SchemaDrift because both are "the file is not what this program was built for".
Then the writing-down. docs/BUILT.md gets the section: the four things the
macro system did not have and now does, each general and none of them
mentioning EDN — a macro reading a file at the call site's path, a package
macro calling its package, one call answering several declarations, and
compile-error, which is the one piece that had to go in the compiler and the
reason it had to. The set rule the real game file decided is there too, and
what defjson shares, which is the design and not the code.
NEXT.md item 9 and PORTING.md §3.9 both close. Not as (read-edn T bytes): the
struct comes from the *file* rather than from a type declared by hand, so the
~80 lines PORTING prices for two schemas are not written at all. The competing
answer PORTING names — compile-time embedding — turned out to be the other half
rather than a competitor: the shape comes from the file at compile time and the
bytes may come from an embed beside it, which is exactly what
test/programs/edn-provide.flan does.
Joseph Ferano
889fdc30d9