// Return the value of a target symbol in this or an outer scope.
public MalVal Get(MalSym keySymbol)
{
Env e = Find(keySymbol);
if (e == null)
{
switch (keySymbol.ToString(true))
{
// Some symbols are only valid when used in a particular context.
case "unquote":
throw new MalEvalError("'unquote' used incorrectly (missing macro?)");
case "quasiquote":
throw new MalEvalError("'quasiquote' used incorrectly (missing macro?)");
case "splice-unquote":
throw new MalEvalError("'splice-unquote' used incorrectly (missing macro?)");
}
//// If here the symbol simply hasn't been defined or is mis-spelt.
throw new MalLookupError("Get - Symbol not found '" + keySymbol.ToString(true) + "'");
}
else
{
if (e.data.TryGetValue(keySymbol.getName(), out MalVal value))
{
return(value);
}
else
{
throw new MalInternalError("Get - Find successful but symbol retrieval failed '" + keySymbol.ToString(true) + "'");
}
}
}
public void Set(MalSym keySymbol, MalVal value)
{
// Takes a symbol key and a mal value and adds them to the environment.
if (!data.TryAdd(keySymbol.getName(), value))
{
// Symbol can shadow an equivalent in an outer scope but cannot be duped.
throw new MalEvalError("Attempt to redefine '" + keySymbol.ToString(true) + "'");
}
}
// Return the value of a target symbol in this or an outer scope.
public MalVal Get(MalSym keySymbol)
{
Env e = Find(keySymbol);
if (e != null && e.data.TryGetValue(keySymbol.getName(), out MalVal value))
{
return(value);
}
throw new MalEvalError("Symbol not found '" + keySymbol.ToString(true) + "'");
}
public Env(Env outer, MalSym binds, MalSym exprs)
{
// TODO - these binds and exprs might not be malsyms
// A key-MalVal dictionary.
data = new Dictionary <string, MalVal>();
// The scope we are created in. Null is taken to mean the REPL itself.
this.outer = outer;
// Bind (set) each element (symbol) to the respective elements of the exprs list
throw new MalInternalError("Env can't bind yet");
}
// Search for and return the environment (scope) that contains a target symbol.
public Env Find(MalSym keySymbol)
{
if (data.ContainsKey(keySymbol.getName()))
{
// Symbol exists in the current scope.
return(this);
}
else if (outer != null)
{
// Recurse to search for the symbol in an outer scope.
return(outer.Find(keySymbol));
}
else
{
// Symbol is not defined.
return(null);
}
}
// Return the value of a target symbol in this or an outer scope.
public MalVal Get(MalSym keySymbol)
{
Env e = Find(keySymbol);
if (e != null && e.data.TryGetValue(keySymbol.getName(), out MalVal value))
{
return(value);
}
switch (keySymbol.ToString(true))
{
case "quote":
throw new MalEvalError("'quote' used where expression expected");
case "quasiquote":
throw new MalEvalError("'quasiquote' used where expression expected");
case "splice-unquote":
throw new MalEvalError("'splice-unquote' used where expression expected");
default:
throw new MalEvalError("Symbol not found '" + keySymbol.ToString(true) + "'");
}
}
// Setup the REPL.
public MalRepl()
{
// Load built-in functions into the initial eval environment.
try
{
myEnv = new Env(null);
// Load core functions.
foreach (var thing in MalNameSpace)
{
MalSym mSym = new MalSym(thing.Key);
if (myEnv.Find(mSym) == null)
{
myEnv.Set(mSym, thing.Value);
}
else
{
// The namespace itself may already have thrown an error but if not.
throw new MalInternalError("Attempt to refine symbol: '" + mSym.ToString(true) + "' with '" + thing.Value.ToString(true) + "'");
}
}
// Load the special eval core function. We have to do it here to access the REPL env.
myEnv.Set(new MalSym("eval"), new MalFunc(args =>
{
return(EVAL(args[0], myEnv));
}));
// some convenient test files
// "F:\Mal-development\mal-tests\mal-step6-test-01.txt"
// "F:\Mal-development\mal-tests\mal-code-01.txt"
// (load-file "F:\Mal-development\mal-tests\mal-code-01.txt")
// (eval (read-string (slurp "F:\Mal-development\mal-tests\mal-code-01.txt")))
// Add 'core' functions defined using Mal itself.
EVAL(READ("(def not (fn (a) (if a false true)))"), myEnv);
// Establish a gensym mechanism
EVAL(READ("(def *gensym-counter* (atom 0))"), myEnv);
EVAL(READ("(def gensym (fn [] (symbol (str \"G__\" (swap *gensym-counter* (fn [x] (+ 1 x)))))))"), myEnv);
EVAL(READ("(def load-file (fn (f) (eval (read-string (str \"(do \" (slurp f) \"))\")))))"), myEnv);
EVAL(READ("(defmacro cond (fn (& xs) (if (> (count xs) 0) (list 'if (first xs) (if (> (count xs) 1) (nth xs 1) (throw \"odd number of forms to cond\")) (cons 'cond (rest (rest xs)))))))"), myEnv);
EVAL(READ("(defmacro or (fn (& xs) (if (empty? xs) nil (if (= 1 (count xs)) (first xs) (let (condvar (gensym)) `(let (~condvar ~(first xs)) (if ~condvar ~condvar (or ~@(rest xs)))))))))"), myEnv);
}
catch (System.TypeInitializationException e)
{
// Typically happens if there is a duplicate symbol in the namespace list
Console.WriteLine("Unrecoverable error: " + e.InnerException.Message);
}
catch (MalLookupError e)
{
Console.WriteLine(e.Message);
}
catch (MalEvalError e)
{
Console.WriteLine(e.Message);
}
catch (MalParseError e)
{
Console.WriteLine(e.Message);
}
}