Implement file-error? and read-error?.

Author: objecthub

README.md

@@ -60,7 +60,6 @@ _LispKit_ is incompatible or incomplete with respect to the following R7RS featu
 
   - Lists are immutable. Mutable cons-cells are supported in a way similar to
     [Racket](https://racket-lang.org)
-  - Error support is incomplete; the following functions are missing: `read-error?`, `file-error?`
   - `current-input-port`, `current-output-port`, and `current-error-port` are functions
     (as required by R5RS) and not parameter objects (as required by R7RS)
   - Datum comments introduced via `#;` do not always work as expected.

Sources/LispKit/Compiler/EvalError.swift

@@ -20,7 +20,6 @@
 
 import Foundation
 
-
 ///
 /// Enumeration `EvalError` represents errors occuring during the evaluation or compilation
 /// of LispKit expressions.

Sources/LispKit/Compiler/RuntimeError.swift

@@ -20,7 +20,6 @@
 
 import Foundation
 
-
 ///
 /// Class `RuntimeError` defines a universal representation of errors in LispKit. A runtime
 /// error consists of the following components:
@@ -411,6 +410,28 @@ public enum ErrorDescriptor: Hashable {
   case abortion
   case custom(String, String)
 
+  
+  public var isFileError: Bool {
+    guard case .eval(let err) = self else {
+      return false
+    }
+    switch err {
+      case .cannotOpenFile, .cannotOpenUrl, .cannotWriteToPort:
+        return true
+      default:
+        return false
+    }
+  }
+  
+  public var isReadError: Bool {
+    switch self {
+      case .lexical(_), .syntax(_):
+        return true
+      default:
+        return false
+    }
+  }
+  
   public var typeDescription: String {
     switch self {
       case .lexical(_):

Sources/LispKit/Compiler/SyntaxError.swift

@@ -20,7 +20,6 @@
 
 import Foundation
 
-
 ///
 /// Enumeration `SyntaxError` represents syntactical errors emitted by the parser.
 ///

Sources/LispKit/Primitives/DynamicControlLibrary.swift

@@ -308,11 +308,17 @@ public final class DynamicControlLibrary: NativeLibrary {
   }
 
   private func isReadError(expr: Expr) -> Expr {
-    return .false
+    guard case .error(let err) = expr else {
+      return .false
+    }
+    return err.descriptor.isReadError ? .true : .false
   }
 
   private func isFileError(expr: Expr) -> Expr {
-    return .false
+    guard case .error(let err) = expr else {
+      return .false
+    }
+    return err.descriptor.isFileError ? .true : .false
   }
 
   private func triggerExit(args: Arguments) throws -> (Procedure, Exprs) {