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-rw-r--r--dhall/src/semantics/tck/typecheck.rs27
1 files changed, 25 insertions, 2 deletions
diff --git a/dhall/src/semantics/tck/typecheck.rs b/dhall/src/semantics/tck/typecheck.rs
index 516ef42..e3ae129 100644
--- a/dhall/src/semantics/tck/typecheck.rs
+++ b/dhall/src/semantics/tck/typecheck.rs
@@ -726,8 +726,31 @@ fn type_one_layer(
record_type.get_type()?,
)
}
- ExprKind::ProjectionByExpr(_, _) => {
- unimplemented!("selection by expression")
+ ExprKind::ProjectionByExpr(record, selection) => {
+ let record_type = record.get_type()?;
+ let rec_kts = match record_type.kind() {
+ ValueKind::RecordType(kts) => kts,
+ _ => return span_err("ProjectionMustBeRecord"),
+ };
+
+ let selection_val = selection.eval(env.as_nzenv());
+ let sel_kts = match selection_val.kind() {
+ ValueKind::RecordType(kts) => kts,
+ _ => return span_err("ProjectionByExprTakesRecordType"),
+ };
+
+ for (l, sel_ty) in sel_kts {
+ match rec_kts.get(l) {
+ Some(rec_ty) => {
+ if rec_ty != sel_ty {
+ return span_err("ProjectionWrongType");
+ }
+ }
+ None => return span_err("ProjectionMissingEntry"),
+ }
+ }
+
+ selection_val
}
ExprKind::Completion(_, _) => unimplemented!("record completion"),
})