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defined the callable interface

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master
Jordan Orelli 12 years ago
parent b387d909b5
commit 1ee8bff82c
2 changed files with 142 additions and 126 deletions
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47
skeam.go
Unescape Escape View File

@ -18,6 +18,10 @@ type sexp struct {
quotelvl int
}
type callable interface {
call(*environment, []interface{}) (interface{}, error)
}
func newSexp() *sexp {
return &sexp{
items: make([]interface{}, 0, 8),
@ -73,12 +77,12 @@ var universe = &environment{map[symbol]interface{}{
// "append"
// special forms
"begin": special(begin),
"define": special(define),
"if": special(_if),
"lambda": special(mklambda),
"quote": special(quote),
"set!": special(set),
symbol(begin.name): begin,
symbol(define.name): define,
symbol(_if.name): _if,
symbol(mklambda.name): mklambda,
symbol(quote.name): quote,
symbol(set.name): set,
}, nil}
// parses the string lexeme into a value that can be eval'd
@ -181,35 +185,14 @@ func eval(v interface{}, env *environment) (interface{}, error) {
return nil, err
}
// check to see if this is a special form
if spec, ok := v.(special); ok {
debugPrint("special!")
if len(t.items) > 1 {
return spec(env, t.items[1:]...)
} else {
return spec(env)
}
}
// exec builtin func if one exists
if b, ok := v.(builtin); ok {
if len(t.items) > 1 {
return b.call(env, t.items[1:])
} else {
return b.call(env, nil)
}
c, ok := v.(callable)
if !ok {
return nil, fmt.Errorf(`expected special form or builtin procedure, received %v`, reflect.TypeOf(v))
}
// exec lambda if possible
if l, ok := v.(lambda); ok {
if len(t.items) > 1 {
return l.call(env, t.items[1:])
} else {
return l.call(env, nil)
}
return c.call(env, t.items[1:])
}
return nil, fmt.Errorf(`expected special form or builtin procedure, received %v`, reflect.TypeOf(v))
return c.call(env, nil)
default:
debugPrint("default eval")

89
special.go
Unescape Escape View File

@ -9,7 +9,37 @@ import (
// type special is a callable outside of the normal execution workflow. That
// is, a special receives its arguments unevaluated, unlike lambdas or builtin,
// both of whose arguments are evaluated upon invocation.
type special func(*environment, ...interface{}) (interface{}, error)
// type special func(*environment, ...interface{}) (interface{}, error)
type special struct {
name string
arity int
variadic bool
fn func(*environment, []interface{}) (interface{}, error)
}
func (s special) checkArity(n int) error {
if n == s.arity {
return nil
}
if s.variadic && n > s.arity {
return nil
}
return arityError{
expected: s.arity,
received: n,
name: s.name,
variadic: s.variadic,
}
}
func (s special) call(env *environment, rawArgs []interface{}) (interface{}, error) {
if err := s.checkArity(len(rawArgs)); err != nil {
return nil, err
}
return s.fn(env, rawArgs)
}
// type arityError is used to store information related to arity errors. That
// is, the invocation of a callable with the wrong number of arguments.
@ -50,11 +80,10 @@ func checkArity(arity int, args []interface{}, name string) error {
// (define x 5)
//
// would create the symbol "x" and set its value to 5.
func define(env *environment, args ...interface{}) (interface{}, error) {
if err := checkArity(2, args, "define"); err != nil {
return nil, err
}
var define = special{
name: "define",
arity: 2,
fn: func(env *environment, args []interface{}) (interface{}, error) {
s, ok := args[0].(symbol)
if !ok {
return nil, fmt.Errorf(`first argument to *define* must be symbol, received %v`, reflect.TypeOf(args[0]))
@ -67,6 +96,7 @@ func define(env *environment, args ...interface{}) (interface{}, error) {
env.set(s, v)
return nil, nil
},
}
// defines the built-in "quote" construct. e.g.:
@ -76,11 +106,10 @@ func define(env *environment, args ...interface{}) (interface{}, error) {
// would evaluate to the list (1 2 3). That is, quote is a function of arity 1
// that is effectively a no-op; the input value is not evaluated, which
// prevents evaluation of the first element of the list, in this case 1.
func quote(_ *environment, args ...interface{}) (interface{}, error) {
if err := checkArity(1, args, "quote"); err != nil {
return nil, err
}
var quote = special{
name: "quote",
arity: 1,
fn: func(_ *environment, args []interface{}) (interface{}, error) {
switch t := args[0].(type) {
case *sexp:
t.quotelvl++
@ -89,6 +118,7 @@ func quote(_ *environment, args ...interface{}) (interface{}, error) {
return &sexp{items: []interface{}{t}, quotelvl: 1}, nil
}
panic("not reached")
},
}
// turns an arbitrary lisp value into a boolean. Apparently the sematics of
@ -110,11 +140,10 @@ func booleanize(v interface{}) bool {
// (if #f "foo" "bar")
//
// would evaluate to "bar"
func _if(env *environment, args ...interface{}) (interface{}, error) {
if err := checkArity(3, args, "if"); err != nil {
return nil, err
}
var _if = special{
name: "if",
arity: 3,
fn: func(env *environment, args []interface{}) (interface{}, error) {
v, err := eval(args[0], env)
if err != nil {
return nil, err
@ -124,6 +153,7 @@ func _if(env *environment, args ...interface{}) (interface{}, error) {
return eval(args[1], env)
}
return eval(args[2], env)
},
}
// defines the built-in "set!" construct, which is used to set the value of an
@ -133,11 +163,10 @@ func _if(env *environment, args ...interface{}) (interface{}, error) {
//
// would set the symbol x to the value 5, if and only if the symbol x was
// previously defined.
func set(env *environment, args ...interface{}) (interface{}, error) {
if err := checkArity(2, args, "set!"); err != nil {
return nil, err
}
var set = special{
name: "set!",
arity: 2,
fn: func(env *environment, args []interface{}) (interface{}, error) {
s, ok := args[0].(symbol)
if !ok {
return nil, fmt.Errorf(`first argument to *set!* must be symbol, received %v`, reflect.TypeOf(args[0]))
@ -154,6 +183,7 @@ func set(env *environment, args ...interface{}) (interface{}, error) {
env.set(s, v)
return nil, nil
},
}
type lambda struct {
@ -190,11 +220,11 @@ func (l lambda) call(env *environment, rawArgs []interface{}) (interface{}, erro
// (lambda (x) (* x x))
//
// would evaluate to a lambda that, when executed, squares its input.
func mklambda(env *environment, args ...interface{}) (interface{}, error) {
var mklambda = special{
name: "lambda",
arity: 2,
fn: func(env *environment, args []interface{}) (interface{}, error) {
debugPrint("mklambda")
if err := checkArity(2, args, "lambda"); err != nil {
return nil, err
}
params, ok := args[0].(*sexp)
if !ok {
@ -216,6 +246,7 @@ func mklambda(env *environment, args ...interface{}) (interface{}, error) {
}
return lambda{env, arglabels, body}, nil
},
}
// defines the built-in "begin" construct. A "begin" statement evaluates each
@ -225,9 +256,11 @@ func mklambda(env *environment, args ...interface{}) (interface{}, error) {
// (begin (+ 1 1) (* 2 2) (+ 3 3))
//
// would evaluate to 6.
func begin(env *environment, args ...interface{}) (interface{}, error) {
var begin = special{
name: "begin",
variadic: true,
fn: func(env *environment, args []interface{}) (interface{}, error) {
debugPrint("begin")
var err error
var v interface{}
for _, arg := range args {
@ -236,6 +269,6 @@ func begin(env *environment, args ...interface{}) (interface{}, error) {
return nil, err
}
}
return v, nil
},
}

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