Simple F# Expression to Java compiler

Compiles simple F# quoted expressions (literals, values, operators, ifs and for loops) to Java code.

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open Microsoft.FSharp.Quotations
open Microsoft.FSharp.Quotations.Patterns
open Microsoft.FSharp.Quotations.DerivedPatterns

let notImplemented () = raise (System.NotImplementedException())

let toTypeName  t =
    if t = typeof<int> then "int"
    elif t = typeof<double> then "double" 
    elif t = typeof<bool> then "boolean"
    else notImplemented()

let rec toJava = function
   | Int32 x -> sprintf "%i" x
   | Double x -> sprintf "%gd" x
   | Bool true -> "true"
   | Bool false -> "false"
   | SpecificCall <@@ (+) @@> (None, _, [lhs;rhs]) -> toOp "+" lhs rhs
   | SpecificCall <@@ (-) @@> (None, _, [lhs;rhs]) -> toOp "-" lhs rhs
   | SpecificCall <@@ (*) @@> (None, _, [lhs;rhs]) -> toOp "*" lhs rhs
   | SpecificCall <@@ (/) @@> (None, _, [lhs;rhs]) -> toOp "/" lhs rhs
   | SpecificCall <@@ (=) @@> (None, _, [lhs;rhs]) -> toOp "==" lhs rhs
   | SpecificCall <@@ (<>) @@> (None, _, [lhs;rhs]) -> toOp "!=" lhs rhs
   | IfThenElse(condition, t, f) -> toIfThenElse condition t f
   | _ -> notImplemented()    
and toOp op lhs rhs =
    sprintf "(%s %s %s)" (toJava lhs) op (toJava rhs)
and toIfThenElse condition t f =
    sprintf "%s ? %s : %s" (toJava condition) (toJava t) (toJava f)

let toClass (expr:Expr<'TRet>)  =
    let returnType = toTypeName typeof<'TRet>
    let body = toJava expr
    sprintf """
public class Generated {
   public static %s fun(){
     return %s;
   }
   public static void main(String []args){
      System.out.println(fun());
   }
}""" returnType body

toClass <@ if 1 + 1 = 2 then 1 else -1 @>

(* Returns
public class Generated {
   public static int fun(){
     return ((1 + 1) == 2) ? 1 : -1;
   }
   public static void main(String []args){
      System.out.println(fun());
   }
}
*)

namespace Microsoft

namespace Microsoft.FSharp

namespace Microsoft.FSharp.Quotations

module Patterns

from Microsoft.FSharp.Quotations

module DerivedPatterns

from Microsoft.FSharp.Quotations

val notImplemented : unit -> 'a

Full name: Script.notImplemented

val raise : exn:System.Exception -> 'T

Full name: Microsoft.FSharp.Core.Operators.raise

namespace System

Multiple items
type NotImplementedException =
inherit SystemException
new : unit -> NotImplementedException + 2 overloads

Full name: System.NotImplementedException

--------------------
System.NotImplementedException() : unit
System.NotImplementedException(message: string) : unit
System.NotImplementedException(message: string, inner: exn) : unit

val toTypeName : t:System.Type -> string

Full name: Script.toTypeName

val t : System.Type

val typeof<'T> : System.Type

Full name: Microsoft.FSharp.Core.Operators.typeof

Multiple items
val int : value:'T -> int (requires member op_Explicit)

Full name: Microsoft.FSharp.Core.Operators.int

--------------------
type int = int32

Full name: Microsoft.FSharp.Core.int

--------------------
type int<'Measure> = int

Full name: Microsoft.FSharp.Core.int<_>

Multiple items
val double : value:'T -> float (requires member op_Explicit)

Full name: Microsoft.FSharp.Core.ExtraTopLevelOperators.double

--------------------
type double = System.Double

Full name: Microsoft.FSharp.Core.double

type bool = System.Boolean

Full name: Microsoft.FSharp.Core.bool

val toJava : _arg1:Expr -> string

Full name: Script.toJava

active recognizer Int32: Expr -> int32 option

Full name: Microsoft.FSharp.Quotations.DerivedPatterns.( |Int32|_| )

val x : int32

val sprintf : format:Printf.StringFormat<'T> -> 'T

Full name: Microsoft.FSharp.Core.ExtraTopLevelOperators.sprintf

active recognizer Double: Expr -> float option

Full name: Microsoft.FSharp.Quotations.DerivedPatterns.( |Double|_| )

val x : float

active recognizer Bool: Expr -> bool option

Full name: Microsoft.FSharp.Quotations.DerivedPatterns.( |Bool|_| )

active recognizer SpecificCall: Expr -> Expr -> (Expr option * System.Type list * Expr list) option

Full name: Microsoft.FSharp.Quotations.DerivedPatterns.( |SpecificCall|_| )

union case Option.None: Option<'T>

val lhs : Expr

val rhs : Expr

val toOp : op:string -> lhs:Expr -> rhs:Expr -> string

Full name: Script.toOp

active recognizer IfThenElse: Expr -> (Expr * Expr * Expr) option

Full name: Microsoft.FSharp.Quotations.Patterns.( |IfThenElse|_| )

val condition : Expr

val t : Expr

val f : Expr

val toIfThenElse : condition:Expr -> t:Expr -> f:Expr -> string

Full name: Script.toIfThenElse

val op : string

val toClass : expr:Expr<'TRet> -> string

Full name: Script.toClass

val expr : Expr<'TRet>

Multiple items
type Expr =
  override Equals : obj:obj -> bool
  member GetFreeVars : unit -> seq<Var>
  member Substitute : substitution:(Var -> Expr option) -> Expr
  member ToString : full:bool -> string
  member CustomAttributes : Expr list
  member Type : Type
  static member AddressOf : target:Expr -> Expr
  static member AddressSet : target:Expr * value:Expr -> Expr
  static member Application : functionExpr:Expr * argument:Expr -> Expr
  static member Applications : functionExpr:Expr * arguments:Expr list list -> Expr
  ...

Full name: Microsoft.FSharp.Quotations.Expr

--------------------
type Expr<'T> =
  inherit Expr
  member Raw : Expr

Full name: Microsoft.FSharp.Quotations.Expr<_>

val returnType : string

val body : string

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More information

Link:	http://fssnip.net/l3
Posted:	1 year ago
Author:	Phillip Trelford
Tags:	java , compiler