go: add step4_if_fn_do

1 files changed, 181 insertions, 0 deletions

diff --git a/go/src/step4_if_fn_do/step4_if_fn_do.go b/go/src/step4_if_fn_do/step4_if_fn_do.go
new file mode 100644
index 0000000..f0cc41f
--- /dev/null
+++ b/go/src/step4_if_fn_do/step4_if_fn_do.go
@@ -0,0 +1,181 @@
+package main
+
+import (
+    "bufio"
+    //"io"
+    "fmt"
+    "os"
+    "strings"
+    "errors"
+)
+
+import (
+    . "types"
+    "reader"
+    "printer"
+    . "env"
+    "core"
+)
+
+// read
+func READ(str string) (MalType, error) {
+    return reader.Read_str(str)
+}
+
+// eval
+func eval_ast(ast MalType, env Env) (MalType, error) {
+    //fmt.Printf("eval_ast: %#v\n", ast)
+    if Symbol_Q(ast) {
+        return env.Get(ast.(Symbol).Val)
+    } else if List_Q(ast) {
+        lst := []MalType{}
+        for _, a := range ast.(List).Val {
+            exp, e := EVAL(a, env)
+            if e != nil { return nil, e }
+            lst = append(lst, exp)
+        }
+        return List{lst}, nil
+    } else if Vector_Q(ast) {
+        lst := []MalType{}
+        for _, a := range ast.(Vector).Val {
+            exp, e := EVAL(a, env)
+            if e != nil { return nil, e }
+            lst = append(lst, exp)
+        }
+        return Vector{lst}, nil
+    } else if Hash_Map_Q(ast) {
+        m := ast.(map[string]MalType)
+        new_hm := map[string]MalType{}
+        for k, v := range m {
+            ke, e1 := EVAL(k, env)
+            if e1 != nil { return nil, e1 }
+            if _, ok := ke.(string); !ok {
+                return nil, errors.New("non string hash-map key")
+            }
+            kv, e2 := EVAL(v, env)
+            if e2 != nil { return nil, e2 }
+            new_hm[ke.(string)] = kv
+        }
+        return new_hm, nil
+    } else {
+        return ast, nil
+    }
+}
+
+func EVAL(ast MalType, env Env) (MalType, error) {
+    //fmt.Printf("EVAL: %#v\n", ast)
+    switch ast.(type) {
+    case List: // continue
+    default:   return eval_ast(ast, env)
+    }
+
+    // apply list
+    a0 := ast.(List).Val[0]
+    var a1 MalType = nil; var a2 MalType = nil
+    switch len(ast.(List).Val) {
+    case 1:
+        a1 = nil; a2 = nil
+    case 2:
+        a1 = ast.(List).Val[1]; a2 = nil
+    default:
+        a1 = ast.(List).Val[1]; a2 = ast.(List).Val[2]
+    }
+    a0sym := "__<*fn*>__"
+    if Symbol_Q(a0) { a0sym = a0.(Symbol).Val } 
+    switch a0sym {
+    case "def!":
+        res, e := EVAL(a2, env)
+        if e != nil { return nil, e }
+        return env.Set(a1.(Symbol).Val, res), nil
+    case "let*":
+        let_env, e := NewEnv(&env, nil, nil)
+        if e != nil { return nil, e }
+        arr1, e := GetSlice(a1)
+        if e != nil { return nil, e }
+        for i := 0; i < len(arr1); i+=2 {
+            if !Symbol_Q(arr1[i]) {
+                return nil, errors.New("non-symbol bind value")
+            }
+            exp, e := EVAL(arr1[i+1], *let_env)
+            if e != nil { return nil, e }
+            let_env.Set(arr1[i].(Symbol).Val, exp)
+        }
+        return EVAL(a2, *let_env)
+    case "do":
+        el, e := eval_ast(List{ast.(List).Val[1:]}, env) 
+        if e != nil { return nil, e }
+        lst := el.(List).Val
+        if len(lst) == 0 { return nil, nil }
+        return lst[len(lst)-1], nil
+    case "if":
+        cond, e := EVAL(a1, env)
+        if e != nil { return nil, e }
+        if cond == nil || cond == false {
+            if len(ast.(List).Val) >= 4 {
+                return EVAL(ast.(List).Val[3], env)
+            } else {
+                return nil, nil
+            }
+        } else {
+            return EVAL(a2, env)
+        }
+    case "fn*":
+        return func(arguments []MalType) (MalType, error) {
+            a1s, e := GetSlice(a1)
+            if e != nil { return nil, e }
+            new_env, e := NewEnv(&env, a1s, arguments)
+            if e != nil { return nil, e }
+            return EVAL(a2, *new_env)
+        }, nil
+    default:
+        el, e := eval_ast(ast, env)
+        if e != nil { return nil, e }
+        f, ok := el.(List).Val[0].(func([]MalType)(MalType, error))
+        if !ok { return nil, errors.New("attempt to call non-function") }
+        return f(el.(List).Val[1:])
+    }
+}
+
+// print
+func PRINT(exp MalType) (MalType, error) {
+    return printer.Pr_str(exp, true), nil
+}
+
+
+var repl_env, _ = NewEnv(nil, nil, nil)
+
+// repl
+func rep(str string) (MalType, error) {
+    var exp MalType
+    var e error
+    if exp, e = READ(str); e != nil { return nil, e }
+    if exp, e = EVAL(exp, *repl_env); e != nil { return nil, e }
+    if exp, e = PRINT(exp); e != nil { return nil, e }
+    return exp, nil
+}
+
+func main() {
+    for k, v := range core.NS {
+        repl_env.Set(k, v)
+    }
+    rep("(def! not (fn* (a) (if a false true)))")
+
+    rdr := bufio.NewReader(os.Stdin);
+    // repl loop
+    for {
+        fmt.Print("user> ");
+        text, err := rdr.ReadString('\n');
+        text = strings.TrimRight(text, "\n");
+        if (err != nil) {
+            return
+        }
+        var out MalType
+        var e error
+        if out, e = rep(text); e != nil {
+            if e.Error() == "<empty line>" { continue }
+            fmt.Printf("Error: %v\n", e)
+            continue
+        }
+        fmt.Printf("%v\n", out)
+    }
+}