public static JymlAST.Cons Eval(JymlAST.Cons exp, JymlEnvironment env)
{
if (exp != null)
{
if (Parser.IsSelfEvaluating(exp))
{
return(new JymlAST.Cons(exp.car, Eval(exp.cdr as JymlAST.Cons, env)));
}
else if (Parser.IsAssignment(exp))
{
return(EvalAssignment(exp, env));
}
else if (Parser.IsDefinition(exp))
{
return(EvalDefinition(exp, env));
}
else if (Parser.IsIf(exp))
{
return(EvalIf(exp, env));
}
else if (Parser.IsLambda(exp))
{
return(MakeLambda(Parser.GetLambdaParameters(exp), Parser.GetLambdaBody(exp), env));
}
else if (Parser.IsBegin(exp))
{
return(EvalSequence(exp.cdr as JymlAST.Cons, env));
}
else if (exp.car is JymlAST.Cons subexp)
{
return(new JymlAST.Cons(Eval(subexp, env), Eval(exp.cdr as JymlAST.Cons, env)));
}
else
{
if (exp.car is string proc)
{
JymlEnvironment.Restraint restraint = env[proc];
if (restraint != null)
{
if (restraint.Value is Procedures || restraint.Value is PrimitiveProcedure)
{
return(Apply(proc, ListOfValues(exp.cdr as JymlAST.Cons, env), env));
}
else
{
return(new JymlAST.Cons(restraint.Value, Eval(exp.cdr as JymlAST.Cons, env)));
}
}
else
{
if (Parser.IsVariable(exp))
{
throw new Exception($"变量 {exp.car} 未定义。");
}
else
{
throw new Exception($"无效的语法：{exp}");
}
}
}
else if (exp.car is JymlAST.Cons cons)
{
return(Apply(cons, ListOfValues(exp.cdr as JymlAST.Cons, env), env));
}
else
{
throw new Exception($"无效的过程调用：{exp}");
}
}
}
else
{
return(null);
}
}
/*
* (define (eval-definition exp env)
* (define-variable! (definition-variable exp)
* (eval (definition-value exp) env)
* env))
*/
private static JymlAST.Cons EvalDefinition(JymlAST.Cons exp, JymlEnvironment env)
{
/*
* (define (definition-variable exp)
* (if [symbol? [mcar [mcdr exp]]]
* [mcar [mcdr exp]]
* [mcar [mcar [mcdr exp]]]))
*/
string defineVariable(JymlAST.Cons c) =>
Parser.IsVariable(c.cdr as JymlAST.Cons) ? (c.cdr as JymlAST.Cons).car as string // 普通变量或 lambda 变量
: ((c.cdr as JymlAST.Cons).car as JymlAST.Cons).car as string; // 过程定义
/*
* (define (definition-value exp)
* (if [symbol? [mcar [mcdr exp]]]
* [mcar [mcdr [mcdr exp]]]
* (make-lambda [mcdr [mcar [mcdr exp]]] ; formal parameters
* [mcdr [mcdr exp]]))) ; body
*/
JymlType defineValue(JymlAST.Cons c)
{
if (Parser.IsVariable(c.cdr as JymlAST.Cons))
{
if (((c.cdr as JymlAST.Cons).cdr as JymlAST.Cons).car is string atom)
{
return(JymlType.CreateType(atom)); // 普通变量或 lambda 变量
}
else if (((c.cdr as JymlAST.Cons).cdr as JymlAST.Cons).car is JymlAST.Cons cons)
{
return(JymlType.CreateType(Eval(cons, env).car)); // 返回一个 value 的子表达式（过程调用）
}
else
{
throw new Exception($"define 表达式 {exp} 的 value 部分只能是一个原子值或一个返回原子值的过程调用。");
}
}
else
{
return(new Procedures(Parser.GetProcedureName(exp), (JymlAST.Cons)Parser.GetLambdaParameters(exp), Parser.GetLambdaBody(exp), env)); // 过程定义
}
}
env.DefineVariable(defineVariable(exp), defineValue(exp));
return(null);
}