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fc7f8a4b00
The test makes more sense in step6. Thanks to kanaka for the read-string suggestion. Introduction of tail call optimization in step5 was making let* affect the parent environment. This was partially fixed in later steps. Introduction of macros in step8 was breaking the evaluation of an empty list. This was fixed by step 9 but never backported.
118 lines
2.8 KiB
Nim
118 lines
2.8 KiB
Nim
import rdstdin, tables, sequtils, types, reader, printer, env, core
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proc read(str: string): MalType = str.read_str
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proc eval(ast: MalType, env: Env): MalType
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proc eval_ast(ast: MalType, env: var Env): MalType =
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case ast.kind
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of Symbol:
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result = env.get(ast.str)
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of List:
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result = list ast.list.mapIt(MalType, it.eval(env))
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of Vector:
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result = vector ast.list.mapIt(MalType, it.eval(env))
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of HashMap:
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result = hash_map()
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for k, v in ast.hash_map.pairs:
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result.hash_map[k] = v.eval(env)
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else:
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result = ast
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proc eval(ast: MalType, env: Env): MalType =
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var ast = ast
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var env = env
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template defaultApply =
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let el = ast.eval_ast(env)
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let f = el.list[0]
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case f.kind
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of MalFun:
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ast = f.malfun.ast
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env = initEnv(f.malfun.env, f.malfun.params, list(el.list[1 .. ^1]))
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else:
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return f.fun(el.list[1 .. ^1])
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while true:
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if ast.kind != List: return ast.eval_ast(env)
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if ast.list.len == 0: return ast
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let a0 = ast.list[0]
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case a0.kind
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of Symbol:
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case a0.str
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of "def!":
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let
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a1 = ast.list[1]
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a2 = ast.list[2]
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return env.set(a1.str, a2.eval(env))
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of "let*":
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let
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a1 = ast.list[1]
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a2 = ast.list[2]
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var let_env = initEnv(env)
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case a1.kind
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of List, Vector:
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for i in countup(0, a1.list.high, 2):
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let_env.set(a1.list[i].str, a1.list[i+1].eval(let_env))
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else: raise newException(ValueError, "Illegal kind in let*")
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ast = a2
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env = let_env
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# Continue loop (TCO)
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of "do":
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let last = ast.list.high
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discard (list ast.list[1 .. <last]).eval_ast(env)
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ast = ast.list[last]
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# Continue loop (TCO)
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of "if":
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let
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a1 = ast.list[1]
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a2 = ast.list[2]
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cond = a1.eval(env)
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if cond.kind in {Nil, False}:
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if ast.list.len > 3: ast = ast.list[3]
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else: ast = nilObj
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else: ast = a2
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of "fn*":
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let
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a1 = ast.list[1]
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a2 = ast.list[2]
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var env2 = env
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let fn = proc(a: varargs[MalType]): MalType =
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var newEnv = initEnv(env2, a1, list(a))
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a2.eval(newEnv)
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return malfun(fn, a2, a1, env)
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else:
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defaultApply()
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else:
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defaultApply()
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proc print(exp: MalType): string = exp.pr_str
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var repl_env = initEnv()
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for k, v in ns.items:
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repl_env.set(k, v)
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# core.nim: defined using nim
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proc rep(str: string): string =
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str.read.eval(repl_env).print
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# core.mal: defined using mal itself
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discard rep "(def! not (fn* (a) (if a false true)))"
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while true:
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try:
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let line = readLineFromStdin("user> ")
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echo line.rep
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except:
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echo getCurrentExceptionMsg()
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echo getCurrentException().getStackTrace()
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