kotlin/src/mal/step2_eval.kt

   1 package mal
   2
   3 fun read(input: String?): MalType = read_str(input)
   4
   5 fun eval(ast: MalType, env: Map<String, MalType>): MalType =
   6     if (ast is MalList) {
   7         val evaluated = eval_ast(ast, env) as ISeq
   8         if (evaluated.first() !is MalFunction) throw MalException("cannot execute non-function")
   9         (evaluated.first() as MalFunction).apply(evaluated.rest())
  10     } else eval_ast(ast, env)
  11
  12 fun eval_ast(ast: MalType, env: Map<String, MalType>): MalType =
  13     if (ast is MalSymbol) {
  14         env.get(ast.value) ?: throw MalException("'${ast.value}' not found")
  15     } else if (ast is MalList) {
  16         ast.elements.fold(MalList(), { a, b -> a.conj_BANG(eval(b, env)); a })
  17     } else if (ast is MalVector) {
  18         ast.elements.fold(MalVector(), { a, b -> a.conj_BANG(eval(b, env)); a })
  19     } else if (ast is MalHashMap) {
  20         ast.elements.entries.fold(MalHashMap(), { a, b -> a.assoc_BANG(b.key, eval(b.value, env)); a })
  21     } else ast
  22
  23 fun print(result: MalType) = pr_str(result, print_readably = true)
  24
  25 fun main(args: Array<String>) {
  26     val env = hashMapOf(
  27             Pair("+", MalFunction({ a: ISeq -> a.seq().reduce({ x, y -> x as MalInteger + y as MalInteger }) })),
  28             Pair("-", MalFunction({ a: ISeq -> a.seq().reduce({ x, y -> x as MalInteger - y as MalInteger }) })),
  29             Pair("*", MalFunction({ a: ISeq -> a.seq().reduce({ x, y -> x as MalInteger * y as MalInteger }) })),
  30             Pair("/", MalFunction({ a: ISeq -> a.seq().reduce({ x, y -> x as MalInteger / y as MalInteger }) }))
  31     )
  32
  33     while (true) {
  34         val input = readline("user> ") ?: break
  35
  36         try {
  37             println(print(eval(read(input), env)))
  38         } catch (e: MalContinue) {
  39         } catch (e: MalException) {
  40             println("Error: " + e.message)
  41         } catch (t: Throwable) {
  42             println("Uncaught " + t + ": " + t.message)
  43         }
  44     }
  45 }