SevicheCC/Lisp-interpreter-in-X
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Fix read_from_token and atom

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This commit is contained in:
Seviche CC 2023-06-10 19:39:28 +08:00
parent cce68e439d
commit fff575908c
Signed by: SevicheCC
GPG key ID: C577000000000000
1 changed files with 16 additions and 27 deletions
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41
TypeScript/lisp.ts
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@ -1,19 +1,19 @@
// Lispts: Scheme Interpreter in TypeScript
const program = '(begin (define r 10) (* pi (* r r)))'
const program = "(begin (define r 10) (* pi (* r r)))"
type LSymbol = Symbol // A Lisp Symbol(alias TSymbol) is implemented as TypeScript string
type LSymbol = string // A Lisp Symbol(alias TSymbol) is implemented as TypeScript string
type LNumber = number // A Lisp Symbol(alias TSymbol) is implemented as TypeScript number
type Atom = LSymbol | number // A Lisp Atom is a Symbol or Number impl
type List = Array<any> // A Lisp List is implemented as a TypeScript array
type Exp = Atom | List // A Lisp expression is an Atom or List
type Env = Object // A Lisp environment is a mapping of {variable: value}
interface Env {
[key: string | number]: any
} // A Lisp environment is a mapping of {variable: value}
class ValueError extends Error{
constructor(message:string) {
super(message)
this.name = 'ValueError'
}
}
/**
* Read a Scheme expression from a string.
*/
const parse = (program: string): Exp => read_from_tokens(tokenize(program))
/**
* Convert a string into a list of tokens.
@ -28,30 +28,20 @@ const tokenize = (char: string): string[] =>
/**
* Numbers become numbers; every other token is a symbol(LSymbol).
*/
const atom = (token: string): Atom => {
try {
if (Number.isNaN(token)) {
throw new ValueError('Value Error')
}
} catch (error) {
if (error === ValueError) {
}
}
}
const atom = (token: string): Atom =>
Number.isNaN(token) ? Number(token) : (token as LSymbol)
/**
* Read an expression from a sequence of tokens
*/
const read_from_tokens = (tokens: string[]): Exp => {
if (tokens.length === 0) {
if (tokens.length === 0 || !tokens) {
throw new Error('unexpected EOF while reading')
}
const token = tokens.shift()
if (token === '(') {
const l = []
while (token[0] !== ')') {
while (tokens[0] !== ')') {
l.push(read_from_tokens(tokens))
}
tokens.shift()
@ -59,9 +49,8 @@ const read_from_tokens = (tokens: string[]): Exp => {
} else if (token === ')') {
throw new Error('unexpected )')
} else {
return atom(token)
return atom(token as string)
}
}
console.log(tokenize(program))
console.log(parse(program))