add AsDouble() (#1906)

Add helpers to say:

`double x = value.AsDouble();`  

or AsDecimal. 

this avoids having to cast and guess whether it's decimal or double.

---------

Co-authored-by: Mike Stall <jmstall@microsoft.com>

src/libraries/Microsoft.PowerFx.Core/Public/Values/FormulaValue.cs

@@ -1,6 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // Licensed under the MIT license.
 
+using System;
 using System.Diagnostics;
 using System.Text;
 using Microsoft.PowerFx.Core.IR;
@@ -88,6 +89,68 @@ public bool TryGetPrimitiveValue(out object val)
 
             val = null;
             return false;
+        }
+
+        public bool AsBoolean()
+        {
+            if (this is BlankValue)
+            {
+                return default;
+            }
+
+            if (TryGetPrimitiveValue(out object val))
+            {
+                if (val is bool b)
+                {
+                    return b;
+                }
+            }
+
+            throw new InvalidOperationException($"Can't coerce to double from {this.Type._type.GetKindString()})");
+        }
+
+        public double AsDouble()
+        {
+            if (this is BlankValue)
+            {
+                return default;
+            }
+
+            if (TryGetPrimitiveValue(out object val))
+            {
+                if (val is double d1)
+                {
+                    return d1;
+                }
+                else if (val is decimal d2)
+                {
+                    return (double)d2;
+                }
+            }
+
+            throw new InvalidOperationException($"Can't coerce to double from {this.Type._type.GetKindString()})");
+        }
+
+        public decimal AsDecimal()
+        {
+            if (this is BlankValue)
+            {
+                return default;
+            }
+
+            if (TryGetPrimitiveValue(out object val))
+            {
+                if (val is double d1)
+                {
+                    return (decimal)d1;
+                }
+                else if (val is decimal d2)
+                {
+                    return d2;
+                }
+            }
+
+            throw new InvalidOperationException($"Can't coerce to decimal from {this.Type._type.GetKindString()})");
         }
     }
 }

src/tests/Microsoft.PowerFx.Interpreter.Tests/ValueTests.cs

@@ -423,6 +423,52 @@ public void TryGetIntTest(double doubleValue, decimal decimalValue, string strin
 
             Assert.False(Library.TryGetInt(str, out int outputStringToInt));
         }
+
+        [Fact]
+        public void AsNumberTests()
+        {
+            NumberValue num = FormulaValue.New((double)1.2);
+            DecimalValue dec = FormulaValue.New(1.2m);
+
+            Assert.Equal(1.2, num.AsDouble());
+            Assert.Equal(1.2, dec.AsDouble());
+
+            Assert.Equal(1.2m, num.AsDecimal());
+            Assert.Equal(1.2m, dec.AsDecimal());
+        }
+
+        [Fact]
+        public void AsNumberTestsBlank()
+        {
+            BlankValue num = FormulaValue.NewBlank(FormulaType.Number);
+            BlankValue dec = FormulaValue.NewBlank(FormulaType.Decimal);
+
+            Assert.Equal(0, num.AsDouble());
+            Assert.Equal(0m, dec.AsDecimal());
+        }
+
+        [Fact]
+        public void AsBooleanTests()
+        {
+            var x = FormulaValue.New(true);
+
+            bool b = x.AsBoolean();
+            Assert.True(x.AsBoolean());
+
+            var x2 = FormulaValue.NewBlank(FormulaType.Boolean);
+            bool b2 = x2.AsBoolean();
+            Assert.False(x2.AsBoolean());
+        }
+
+        [Fact]
+        public void AsNumberFailTests()
+        {
+            StringValue num = FormulaValue.New("1.2");
+
+            Assert.Throws<InvalidOperationException>(() => num.AsDouble());
+            Assert.Throws<InvalidOperationException>(() => num.AsDecimal());
+            Assert.Throws<InvalidOperationException>(() => num.AsBoolean());
+        }
     }
 
     public static class FormulaValueExtensions