Last active
October 4, 2022 02:34
-
-
Save zehnpaard/f1aa570715dacab7d0de26bdcb9d033b to your computer and use it in GitHub Desktop.
Simple Bool from Types and Programming Languages, simplified based on https://github.com/hsk/simpletapl
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
type ty = | |
| TArrow of ty * ty | |
| TBool | |
type exp = | |
| EVar of string | |
| EAbs of string * ty * exp | |
| EApp of exp * exp | |
| ETrue | |
| EFalse | |
| EIf of exp * exp * exp | |
let rec typeof env = function | |
| EVar var -> List.assoc var env | |
| EAbs(var, t1, e1) -> TArrow(t1, typeof ((var,t1)::env) e1) | |
| EApp(e1, e2) -> | |
(match typeof env e1 with | |
| TArrow(t11, t12) where t11 = typeof env e2 -> t12 | |
| TArrow _ -> failwith "parameter type mismatch" | |
| _ -> failwith "non-arrow type in function position") | |
| ETrue | EFalse -> TBool | |
| EIf(e1,e2,e3) -> | |
if typeof env e1 != TBool | |
then failwith "guard of conditional not boolean" | |
else | |
let t2 = typeof env e2 in | |
if typeof env e3 != t2 then failwith "type mismatch in arms of conditional" | |
else t2 |
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment