[SOLVED] 程序代写 (* Winter 2012 *)

(* Winter 2012 *)
(* Code for Lecture 1: Evaluation and Typing *)

(* Integers *)

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(-1 : int) ;;
( 4 : int) ;;
5 / 2 ;; (* Result: 2 : int *)

(* Reals *)
(3.14 : float);;

((5.0 /. 2.0) : float);; (* NOT 5 / 2 and NOT 5.0 / 2.0 *)

(* Type errors
# 5 / 3.0;;
Characters 4-7:
Error: This expression has type float but an expression was expected of type

# 5.0 / 3;;
Characters 0-3:
Error: This expression has type float but an expression was expected of type

# 5 /. 3;;
Characters 0-1:
Error: This expression has type int but an expression was expected of type

(* Booleans *)
(true : bool);;
(false : bool);;

if 0 = 0 then 1.0 else 2.0 ;;
(* = tests structural equality *)

if true then 4.0 else 1.0 /. 0.0 ;;
(* NOTE: division by 0.0 is not caught statically during type checking *)

(* Type error
# if 0 = 1 then 1 else 2.0;;
Characters 21-24:
if 0 = 1 then 1 else 2.0;;
Error: This expression has type float but an expression was expected of type

(* Typing and Evaluation *)
(* Some ill-typed expressions *)
# 2.0 + 1;;
Characters 0-3:
Error: This expression has type float but an expression was expected of type

(* Some well-typed expressions without a value *)
Exception: Division_by_zero.

# if 1 / 0 = 0 then true else false ;;
Exception: Division_by_zero.

# if false then 4 else 1 / 0 ;;
Exception: Division_by_zero.

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