mal/swift3/Sources/step4_if_fn_do/main.swift

import Foundation

// read
func READ(_ str: String) throws -> MalVal {
    return try read_str(str)
}

// eval
func eval_ast(_ ast: MalVal, _ env: Env) throws -> MalVal {
    switch ast {
    case MalVal.MalSymbol:
        return try env.get(ast)
    case MalVal.MalList(let lst, _):
        return list(try lst.map { try EVAL($0, env) })
    case MalVal.MalVector(let lst, _):
        return vector(try lst.map { try EVAL($0, env) })
    case MalVal.MalHashMap(let dict, _):
        var new_dict = Dictionary<String,MalVal>()
        for (k,v) in dict { new_dict[k] = try EVAL(v, env) }
        return hash_map(new_dict)
    default:
        return ast
    }
}

func EVAL(_ ast: MalVal, _ env: Env) throws -> MalVal {
    switch ast {
    case MalVal.MalList(let lst, _): if lst.count == 0 { return ast }
    default: return try eval_ast(ast, env)
    }

    switch ast {
    case MalVal.MalList(let lst, _):
        switch lst[0] {
        case MalVal.MalSymbol("def!"):
            return try env.set(lst[1], try EVAL(lst[2], env))
        case MalVal.MalSymbol("let*"):
            let let_env = try Env(env)
            var binds = Array<MalVal>()
            switch lst[1] {
            case MalVal.MalList(let l, _): binds = l
            case MalVal.MalVector(let l, _): binds = l
            default:
                throw MalError.General(msg: "Invalid let* bindings")
            }
            var idx = binds.startIndex
            while idx < binds.endIndex {
                let v = try EVAL(binds[binds.index(after: idx)], let_env)
                try let_env.set(binds[idx], v)
                idx = binds.index(idx, offsetBy: 2)
            }
            return try EVAL(lst[2], let_env)
        case MalVal.MalSymbol("do"):
            let slc = lst[lst.index(after: lst.startIndex)..<lst.endIndex]
            switch try eval_ast(list(Array(slc)), env) {
            case MalVal.MalList(let elst, _):
                return elst[elst.index(before: elst.endIndex)]
            default:
                throw MalError.General(msg: "Invalid do form")
            }
        case MalVal.MalSymbol("if"):
            switch try EVAL(lst[1], env) {
            case MalVal.MalFalse, MalVal.MalNil:
                if lst.count > 3 {
                    return try EVAL(lst[3], env)
                } else {
                    return MalVal.MalNil
                }
            default:
                return try EVAL(lst[2], env)
            }
        case MalVal.MalSymbol("fn*"):
            return malfunc( {
                return try EVAL(lst[2], Env(env, binds: lst[1],
                                                 exprs: list($0)))
            })
        default:
            switch try eval_ast(ast, env) {
            case MalVal.MalList(let elst, _):
                switch elst[0] {
                case MalVal.MalFunc(let fn,_,_,_,_,_):
                    let args = Array(elst[1..<elst.count])
                    return try fn(args)
                default:
                    throw MalError.General(msg: "Cannot apply on '\(elst[0])'")
                }
            default: throw MalError.General(msg: "Invalid apply")
            }
        }
    default:
        throw MalError.General(msg: "Invalid apply")
    }
}

// print
func PRINT(_ exp: MalVal) -> String {
    return pr_str(exp, true)
}


// repl
@discardableResult
func rep(_ str:String) throws -> String {
    return PRINT(try EVAL(try READ(str), repl_env))
}

var repl_env: Env = try Env()

// core.swift: defined using Swift
for (k, fn) in core_ns {
    try repl_env.set(MalVal.MalSymbol(k), malfunc(fn))
}

// core.mal: defined using the language itself
try rep("(def! not (fn* (a) (if a false true)))")


while true {
    print("user> ", terminator: "")
    let line = readLine(strippingNewline: true)
    if line == nil { break }
    if line == "" { continue }

    do {
        print(try rep(line!))
    } catch (MalError.Reader(let msg)) {
        print("Error: \(msg)")
    } catch (MalError.General(let msg)) {
        print("Error: \(msg)")
    }
}