address remaining TODO, fix issues with left-nesting for for and ext, add motivation blurb to the readme

1 files changed, 5 insertions, 2 deletions

diff --git a/src/checker_set.rs b/src/checker_set.rs
index 98e10ec..a00ea81 100644
--- a/src/checker_set.rs
+++ b/src/checker_set.rs
@@ -1,7 +1,7 @@
 use crate::ast::*;
 use crate::checker_state::*;
 
-use std::collections::HashMap;
+use std::collections::{HashMap, HashSet};
 use tracing::instrument;
 
 impl CheckerState {
@@ -11,6 +11,10 @@ impl CheckerState {
             Set::BuiltIn(_) => Ok(set.clone()),
             Set::Record(fields) => {
                 let mut ctx = self.clone();
+                let field_set = fields.iter().map(|f| &f.name).collect::<HashSet<&String>>();
+                if field_set.len() != fields.len() {
+                    todo!("duplicate fields");
+                }
                 let fields = fields
                     .into_iter()
                     .map(|Field { name, carries }| {
@@ -260,7 +264,6 @@ impl CheckerState {
                 })
             }
             Element::Case { arms, scrutinee } => {
-                // TODO: do we allow mapping out of bottom?
                 if arms.is_empty() {
                     return Err(CheckerError::Unimplemented(
                         "mapping out of bottom types".to_string(),