(FeDRO)['infinte']

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;


namespace Parabola_closure_ex {
    public delegate double MathFunction(double x);
    class Program {
        static MathFunction para(double a, double b, double c) {
            return x => a * x * x + b * x + c;
        }
        static void Main(string[] args) {
            MathFunction f;
            f = para(1, 2, 3);
            Console.WriteLine(f(3));
            Console.ReadKey();
        }
    }
}

var para = function(a, b, c) {
    return function(x) {
        return a * x * x + b * x + c;
    }
};


//main
var f = para(1, 2, 3);
alert(f(3));

IL:

.assembly extern mscorlib
{
  .publickeytoken = (B7 7A 5C 56 19 34 E0 89 )                         // .z\V.4..
  .ver 2:0:0:0
}
.assembly Parabola_closure_ex
{
  .custom instance void [mscorlib]System.Reflection.AssemblyCopyrightAttribute::.ctor(string) = ( 01 00 1B 43 6F 70 79 72 69 67 68 74 20 C2 A9 20   // ...Copyright ..
                                                                                                  4D 69 63 72 6F 73 6F 66 74 20 32 30 30 39 00 00 ) // Microsoft 2009..
  .custom instance void [mscorlib]System.Reflection.AssemblyTitleAttribute::.ctor(string) = ( 01 00 13 50 61 72 61 62 6F 6C 61 5F 63 6C 6F 73   // ...Parabola_clos
                                                                                              75 72 65 5F 65 78 00 00 )                         // ure_ex..
  .custom instance void [mscorlib]System.Reflection.AssemblyDescriptionAttribute::.ctor(string) = ( 01 00 00 00 00 )
  .custom instance void [mscorlib]System.Reflection.AssemblyConfigurationAttribute::.ctor(string) = ( 01 00 00 00 00 )
  .custom instance void [mscorlib]System.Reflection.AssemblyCompanyAttribute::.ctor(string) = ( 01 00 09 4D 69 63 72 6F 73 6F 66 74 00 00 )       // ...Microsoft..
  .custom instance void [mscorlib]System.Reflection.AssemblyProductAttribute::.ctor(string) = ( 01 00 13 50 61 72 61 62 6F 6C 61 5F 63 6C 6F 73   // ...Parabola_clos
                                                                                                75 72 65 5F 65 78 00 00 )                         // ure_ex..
  .custom instance void [mscorlib]System.Runtime.InteropServices.GuidAttribute::.ctor(string) = ( 01 00 24 37 37 38 64 38 37 32 35 2D 36 36 64 38   // ..$778d8725-66d8
                                                                                                  2D 34 66 36 33 2D 38 39 66 39 2D 35 63 31 61 62   // -4f63-89f9-5c1ab
                                                                                                  30 31 65 66 66 66 66 00 00 )                      // 01effff..
  .custom instance void [mscorlib]System.Reflection.AssemblyTrademarkAttribute::.ctor(string) = ( 01 00 00 00 00 )
  .custom instance void [mscorlib]System.Runtime.InteropServices.ComVisibleAttribute::.ctor(bool) = ( 01 00 00 00 00 ) 
  // --- 下列自定义属性会自动添加，不要取消注释 -------
  //  .custom instance void [mscorlib]System.Diagnostics.DebuggableAttribute::.ctor(valuetype [mscorlib]System.Diagnostics.DebuggableAttribute/DebuggingModes) = ( 01 00 07 01 00 00 00 00 ) 
  .custom instance void [mscorlib]System.Runtime.CompilerServices.RuntimeCompatibilityAttribute::.ctor() = ( 01 00 01 00 54 02 16 57 72 61 70 4E 6F 6E 45 78   // ....T..WrapNonEx
                                                                                                             63 65 70 74 69 6F 6E 54 68 72 6F 77 73 01 )       // ceptionThrows.
  .custom instance void [mscorlib]System.Reflection.AssemblyFileVersionAttribute::.ctor(string) = ( 01 00 07 31 2E 30 2E 30 2E 30 00 00 )             // ...1.0.0.0..
  .custom instance void [mscorlib]System.Runtime.CompilerServices.CompilationRelaxationsAttribute::.ctor(int32) = ( 01 00 08 00 00 00 00 00 )
  .hash algorithm 0x00008004
  .ver 1:0:0:0
}
.module Parabola_closure_ex.exe
// MVID: {7393789F-0AC1-4607-976B-989DAF5B969E}
.imagebase 0x00400000
.file alignment 0x00000200
.stackreserve 0x00100000
.subsystem 0x0003       // WINDOWS_CUI
.corflags 0x00000001    //  ILONLY
// Image base: 0x0000000000890000
// =============== CLASS MEMBERS DECLARATION ===================
.class public auto ansi sealed Parabola_closure_ex.MathFunction
       extends [mscorlib]System.MulticastDelegate
{
  .method public hidebysig specialname rtspecialname
          instance void  .ctor(object 'object',
                               native int 'method') runtime managed
  {
  } // end of method MathFunction::.ctor
  .method public hidebysig newslot virtual
          instance float64  Invoke(float64 x) runtime managed
  {
  } // end of method MathFunction::Invoke
  .method public hidebysig newslot virtual
          instance class [mscorlib]System.IAsyncResult
          BeginInvoke(float64 x,
                      class [mscorlib]System.AsyncCallback callback,
                      object 'object') runtime managed
  {
  } // end of method MathFunction::BeginInvoke
  .method public hidebysig newslot virtual
          instance float64  EndInvoke(class [mscorlib]System.IAsyncResult result) runtime managed
  {
  } // end of method MathFunction::EndInvoke
} // end of class Parabola_closure_ex.MathFunction
.class private auto ansi beforefieldinit Parabola_closure_ex.Program
       extends [mscorlib]System.Object
{
  .class auto ansi sealed nested private beforefieldinit '<>c__DisplayClass1'
         extends [mscorlib]System.Object
  {
    .custom instance void [mscorlib]System.Runtime.CompilerServices.CompilerGeneratedAttribute::.ctor() = ( 01 00 00 00 )
    .field public float64 a
    .field public float64 b
    .field public float64 c
    .method public hidebysig specialname rtspecialname
            instance void  .ctor() cil managed
    {
      // 代码大小       7 (0x7)
      .maxstack  8
      IL_0000:  ldarg.0
      IL_0001:  call       instance void [mscorlib]System.Object::.ctor()
      IL_0006:  ret
    } // end of method '<>c__DisplayClass1'::.ctor
    .method public hidebysig instance float64
            '
b__0'(float64 x) cil managed
    {
      // 代码大小       31 (0x1f)
      .maxstack  3
      .locals init ([0] float64 CS$1$0000)
      IL_0000:  ldarg.0
      IL_0001:  ldfld      float64 Parabola_closure_ex.Program/'<>c__DisplayClass1'::a
      IL_0006:  ldarg.1
      IL_0007:  mul
      IL_0008:  ldarg.1
      IL_0009:  mul
      IL_000a:  ldarg.0
      IL_000b:  ldfld      float64 Parabola_closure_ex.Program/'<>c__DisplayClass1'::b
      IL_0010:  ldarg.1
      IL_0011:  mul
      IL_0012:  add
      IL_0013:  ldarg.0
      IL_0014:  ldfld      float64 Parabola_closure_ex.Program/'<>c__DisplayClass1'::c
      IL_0019:  add
      IL_001a:  stloc.0
      IL_001b:  br.s       IL_001d
      IL_001d:  ldloc.0
      IL_001e:  ret
    } // end of method '<>c__DisplayClass1'::'
b__0'
  } // end of class '<>c__DisplayClass1'
  .method private hidebysig static class Parabola_closure_ex.MathFunction
          para(float64 a,
               float64 b,
               float64 c) cil managed
  {
    // 代码大小       45 (0x2d)
    .maxstack  3
    .locals init ([0] class Parabola_closure_ex.Program/'<>c__DisplayClass1' 'CS$<>8__locals2',
             [1] class Parabola_closure_ex.MathFunction CS$1$0000)
    IL_0000:  newobj     instance void Parabola_closure_ex.Program/'<>c__DisplayClass1'::.ctor()
    IL_0005:  stloc.0
    IL_0006:  ldloc.0
    IL_0007:  ldarg.0
    IL_0008:  stfld      float64 Parabola_closure_ex.Program/'<>c__DisplayClass1'::a
    IL_000d:  ldloc.0
    IL_000e:  ldarg.1
    IL_000f:  stfld      float64 Parabola_closure_ex.Program/'<>c__DisplayClass1'::b
    IL_0014:  ldloc.0
    IL_0015:  ldarg.2
    IL_0016:  stfld      float64 Parabola_closure_ex.Program/'<>c__DisplayClass1'::c
    IL_001b:  nop
    IL_001c:  ldloc.0
    IL_001d:  ldftn      instance float64 Parabola_closure_ex.Program/'<>c__DisplayClass1'::'
b__0'(float64)
    IL_0023:  newobj     instance void Parabola_closure_ex.MathFunction::.ctor(object,
                                                                               native int)
    IL_0028:  stloc.1
    IL_0029:  br.s       IL_002b
    IL_002b:  ldloc.1
    IL_002c:  ret
  } // end of method Program::para
  .method private hidebysig static void  Main(string[] args) cil managed
  {
    .entrypoint
    // 代码大小       62 (0x3e)
    .maxstack  3
    .locals init ([0] class Parabola_closure_ex.MathFunction f)
    IL_0000:  nop
    IL_0001:  ldc.r8     1.
    IL_000a:  ldc.r8     2.
    IL_0013:  ldc.r8     3.
    IL_001c:  call       class Parabola_closure_ex.MathFunction Parabola_closure_ex.Program::para(float64,
                                                                                                  float64,
                                                                                                  float64)
    IL_0021:  stloc.0
    IL_0022:  ldloc.0
    IL_0023:  ldc.r8     3.
    IL_002c:  callvirt   instance float64 Parabola_closure_ex.MathFunction::Invoke(float64)
    IL_0031:  call       void [mscorlib]System.Console::WriteLine(float64)
    IL_0036:  nop
    IL_0037:  call       valuetype [mscorlib]System.ConsoleKeyInfo [mscorlib]System.Console::ReadKey()
    IL_003c:  pop
    IL_003d:  ret
  } // end of method Program::Main
  .method public hidebysig specialname rtspecialname
          instance void  .ctor() cil managed
  {
    // 代码大小       7 (0x7)
    .maxstack  8
    IL_0000:  ldarg.0
    IL_0001:  call       instance void [mscorlib]System.Object::.ctor()
    IL_0006:  ret
  } // end of method Program::.ctor
} // end of class Parabola_closure_ex.Program

请注意那个“<>c__DisplayClass1”，闭包就这样看到啦！