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71 lines
2.3 KiB
OCaml
71 lines
2.3 KiB
OCaml
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(* Opening a library for generic programming (https://github.com/dboulytchev/GT).
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The library provides "@type ..." syntax extension and plugins like show, etc.
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*)
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open GT
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(* Simple expressions: syntax and semantics *)
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module Expr =
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struct
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(* The type for expressions. Note, in regular OCaml there is no "@type..."
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notation, it came from GT.
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*)
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@type t =
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(* integer constant *) | Const of int
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(* variable *) | Var of string
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(* binary operator *) | Binop of string * t * t with show
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(* Available binary operators:
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!! --- disjunction
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&& --- conjunction
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==, !=, <=, <, >=, > --- comparisons
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+, - --- addition, subtraction
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*, /, % --- multiplication, division, reminder
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*)
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(* State: a partial map from variables to integer values. *)
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type state = string -> int
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(* Empty state: maps every variable into nothing. *)
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let empty = fun x -> failwith (Printf.sprintf "Undefined variable %s" x)
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(* Update: non-destructively "modifies" the state s by binding the variable x
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to value v and returns the new state.
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*)
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let update x v s = fun y -> if x = y then v else s y
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(* Expression evaluator
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val eval : state -> t -> int
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Takes a state and an expression, and returns the value of the expression in
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the given state.
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*)
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let eval _ = failwith "Not implemented yet"
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end
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(* Simple statements: syntax and sematics *)
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module Stmt =
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struct
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(* The type for statements *)
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@type t =
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(* read into the variable *) | Read of string
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(* write the value of an expression *) | Write of Expr.t
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(* assignment *) | Assign of string * Expr.t
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(* composition *) | Seq of t * t with show
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(* The type of configuration: a state, an input stream, an output stream *)
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type config = Expr.state * int list * int list
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(* Statement evaluator
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val eval : config -> t -> config
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Takes a configuration and a statement, and returns another configuration
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*)
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let eval _ = failwith "Not implemented yet"
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end
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