r/step4_if_fn_do.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     #cat("EVAL: ", .pr_str(ast,TRUE), "\n", sep="")
  26     if (!.list_q(ast)) {
  27         return(eval_ast(ast, env))
  28     }
  29
  30     # apply list
  31     switch(paste("l",length(ast),sep=""),
  32            l0={ return(ast) },
  33            l1={ a0 <- ast[[1]]; a1 <- NULL; a2 <- NULL },
  34            l2={ a0 <- ast[[1]]; a1 <- ast[[2]]; a2 <- NULL },
  35            { a0 <- ast[[1]]; a1 <- ast[[2]]; a2 <- ast[[3]] })
  36     if (length(a0) > 1) a0sym <- "__<*fn*>__"
  37     else                a0sym <- as.character(a0)
  38     if (a0sym == "def!") {
  39         res <- EVAL(ast[[3]], env)
  40         return(Env.set(env, a1, res))
  41     } else if (a0sym == "let*") {
  42         let_env <- new.Env(env)
  43         for(i in seq(1,length(a1),2)) {
  44             Env.set(let_env, a1[[i]], EVAL(a1[[i+1]], let_env))
  45         }
  46         return(EVAL(a2, let_env))
  47     } else if (a0sym == "do") {
  48         el <- eval_ast(slice(ast,2), env)
  49         return(el[[length(el)]])
  50     } else if (a0sym == "if") {
  51         cond <- EVAL(a1, env)
  52         if (.nil_q(cond) || identical(cond, FALSE)) {
  53             if (length(ast) < 4) return(nil)
  54             return(EVAL(ast[[4]], env))
  55         } else {
  56             return(EVAL(a2, env))
  57         }
  58     } else if (a0sym == "fn*") {
  59         return(function(...) {
  60             EVAL(a2, new.Env(env, a1, list(...)))
  61         })
  62     } else {
  63         el <- eval_ast(ast, env)
  64         f <- el[[1]]
  65         return(do.call(f,slice(el,2)))
  66     }
  67 }
  68
  69 PRINT <- function(exp) {
  70     return(.pr_str(exp, TRUE))
  71 }
  72
  73 repl_env <- new.Env()
  74 rep <- function(str) return(PRINT(EVAL(READ(str), repl_env)))
  75
  76 # core.r: defined using R
  77 for(k in names(core_ns)) { Env.set(repl_env, k, core_ns[[k]]) }
  78
  79 # core.mal: defined using the language itself
  80 . <- rep("(def! not (fn* (a) (if a false true)))")
  81
  82
  83 repeat {
  84     line <- readline("user> ")
  85     if (is.null(line)) { cat("\n"); break }
  86     tryCatch({
  87         cat(rep(line),"\n", sep="")
  88     }, error=function(err) {
  89         cat("Error: ", get_error(err),"\n", sep="")
  90     })
  91     # R debug/fatal with tracebacks:
  92     #cat(rep(line),"\n", sep="")
  93 }