diff options
| -rw-r--r-- | stlc-let.rkt | 21 |
1 files changed, 16 insertions, 5 deletions
diff --git a/stlc-let.rkt b/stlc-let.rkt index 1c2453f..82d7a5f 100644 --- a/stlc-let.rkt +++ b/stlc-let.rkt @@ -46,14 +46,22 @@ (match with [`(→ ,a ,b) (check body b (dict-set ctx id a))] [_ (err (format "expected → type to check λ with but received ~a" with))])] + [`((λ ,id ,body) ,arg) + (note "unable to check arg type from λ lacking annotation") + (check body with ctx)] ; hmm + [`(λ ,id (: ,type) ,body) + (and (check `(λ ,id ,body) type ctx) (equiv with type))] [`((λ ,id (: (→ ,a ,b)) ,body) ,arg) (and (check arg a ctx) (equiv with b) (check `(λ ,id ,body) `(→ ,a ,b) (dict-set ctx id a)))] - [`(let ,id ,expr ,body) ; desugaring + ; desugaring and error handling + [`(let ,id ,expr ,body) (check `((λ ,id ,body) ,expr) with ctx)] [`(let ,id (: ,type) ,expr ,body) (check `((λ ,id (: ,type) ,body) ,expr) with ctx)] - [`((λ ,id ,body) (: ,type) ,arg) ; error handling + [`(λ ,id (: ,type) ,body) + (err (format "expected → type on λ but received ~a" type))] + [`((λ ,id (: ,type) ,body) ,arg) (err (format "expected → type on λ but received ~a" type))] [expr (err (format "inferring an unknown expression ~a" expr))])) @@ -73,7 +81,7 @@ [`((λ ,id ,body) ,arg) (infer body (dict-set ctx id (infer arg ctx)))] [`(λ ,id (: (→ ,a ,b)) ,body) - (note "arg types are unable to be inferred") + (note "unable to infer arg type from λ lacking annotation") (if (check body b (dict-set ctx id a)) `(→ ,a ,b) (err (format "inferred return type of ~a does not match annotated type ~a" @@ -88,8 +96,11 @@ [`(let ,id (: ,type) ,expr ,body) (infer `((λ ,id (: ,type) ,expr) ,body) ctx)] [`(λ ,id ,body) ; error handling - (err "unable to infer type from a function")] - [`(: ,type) (err "inferring from a type annotation")] + (err "unable to infer type from λ lacking annotation")] ; hmm + [`(λ ,id (: ,type) ,body) + (err (format "expected → type on λ but received ~a" type))] + [`((λ ,id (: ,type) ,body) ,arg) + (err (format "expected → type on λ but received ~a" type))] [expr (err (format "inferring an unknown expression ~a" expr))])) (define (dict-get dict key) |