r/step5_tco.r

   1 if(!exists("..readline..")) source("readline.r")
   2 if(!exists("..types..")) source("types.r")
   3 if(!exists("..reader..")) source("reader.r")
   4 if(!exists("..printer..")) source("printer.r")
   5 if(!exists("..env..")) source("env.r")
   6 if(!exists("..core..")) source("core.r")
   7
   8 READ <- function(str) {
   9     return(read_str(str))
  10 }
  11
  12 eval_ast <- function(ast, env) {
  13     if (.symbol_q(ast)) {
  14         Env.get(env, ast)
  15     } else if (.list_q(ast)) {
  16         new.listl(lapply(ast, function(a) EVAL(a, env)))
  17     } else if (.vector_q(ast)) {
  18         new.vectorl(lapply(ast, function(a) EVAL(a, env)))
  19     } else {
  20         ast
  21     }
  22 }
  23
  24 EVAL <- function(ast, env) {
  25     repeat {
  26
  27     #cat("EVAL: ", .pr_str(ast,TRUE), "\n", sep="")
  28     if (!.list_q(ast)) {
  29         return(eval_ast(ast, env))
  30     }
  31
  32     # apply list
  33     switch(paste("l",length(ast),sep=""),
  34            l0={ return(ast) },
  35            l1={ a0 <- ast[[1]]; a1 <- NULL;     a2 <- NULL },
  36            l2={ a0 <- ast[[1]]; a1 <- ast[[2]]; a2 <- NULL },
  37               { a0 <- ast[[1]]; a1 <- ast[[2]]; a2 <- ast[[3]] })
  38     if (length(a0) > 1) a0sym <- "__<*fn*>__"
  39     else                a0sym <- as.character(a0)
  40     if (a0sym == "def!") {
  41         res <- EVAL(a2, env)
  42         return(Env.set(env, a1, res))
  43     } else if (a0sym == "let*") {
  44         let_env <- new.Env(env)
  45         for(i in seq(1,length(a1),2)) {
  46             Env.set(let_env, a1[[i]], EVAL(a1[[i+1]], let_env))
  47         }
  48         ast <- a2
  49         env <- let_env
  50     } else if (a0sym == "do") {
  51         eval_ast(slice(ast,2,length(ast)-1), env)
  52         ast <- ast[[length(ast)]]
  53     } else if (a0sym == "if") {
  54         cond <- EVAL(a1, env)
  55         if (.nil_q(cond) || identical(cond, FALSE)) {
  56             if (length(ast) < 4) return(NULL)
  57             ast <- ast[[4]]
  58         } else {
  59             ast <- a2
  60         }
  61     } else if (a0sym == "fn*") {
  62         return(malfunc(a2, env, a1))
  63     } else {
  64         el <- eval_ast(ast, env)
  65         f <- el[[1]]
  66         if (class(f) == "MalFunc") {
  67             ast <- f$ast
  68             env <- f$gen_env(slice(el,2))
  69         } else {
  70             return(do.call(f,slice(el,2)))
  71         }
  72     }
  73
  74     }
  75 }
  76
  77 PRINT <- function(exp) {
  78     return(.pr_str(exp, TRUE))
  79 }
  80
  81 repl_env <- new.Env()
  82 rep <- function(str) return(PRINT(EVAL(READ(str), repl_env)))
  83
  84 # core.r: defined using R
  85 for(k in names(core_ns)) { Env.set(repl_env, k, core_ns[[k]]) }
  86
  87 # core.mal: defined using the language itself
  88 . <- rep("(def! not (fn* (a) (if a false true)))")
  89
  90
  91 repeat {
  92     line <- readline("user> ")
  93     if (is.null(line)) { cat("\n"); break }
  94     tryCatch({
  95         cat(rep(line),"\n", sep="")
  96     }, error=function(err) {
  97         cat("Error: ", get_error(err),"\n", sep="")
  98     })
  99     # R debug/fatal with tracebacks:
 100     #cat(rep(line),"\n", sep="")
 101 }