Add eval

.vscode/settings.json

@@ -2,5 +2,6 @@
   "[python]": {
     "editor.defaultFormatter": "ms-python.autopep8"
   },
-  "python.formatting.provider": "none"
+  "python.formatting.provider": "none",
+  "cSpell.words": ["expt"]
 }

Python3/lisp.py

@@ -3,7 +3,7 @@ import math
 import operator as op
 
 program = "(begin (define r 10) (* pi (* r r)))"
-# Types
+################ Types
 
 Symbol = str
 List = list
@@ -12,19 +12,16 @@ Atom = (Symbol, Number)
 Exp = (Atom, list)
 Env = dict
 
-# Parsing: parse, tokenize, and read_from_tokens
-
+################ Parsing: parse, tokenize, and read_from_tokens
 
 def parse(program: str) -> Exp:
     "Read a Scheme expression from a string."
     return read_from_tokens(tokenize(program))
 
-
 def tokenize(chars: str) -> list:
     "Convert a string of characters into list of tokens."
     return chars.replace('(', ' ( ').replace(')', ' ) ').split()
 
-
 def read_from_tokens(tokens: list) -> Exp:
     "Read an expression from a sequence of tokens."
     if len(tokens) == 0:
@@ -41,7 +38,6 @@ def read_from_tokens(tokens: list) -> Exp:
     else:
         return atom(token)
 
-
 def atom(token: str) -> Atom:
     "Numbers become numbers; every other token is a symbol."
     try:
@@ -82,8 +78,32 @@ def standard_env() -> Env:
         'print': print,
         'procedure?': callable,
         'round': round,
-        'symbol?': lambda x : isinstance(x, Symbol)
+        'symbol?': lambda x : isinstance(x, Symbol),
+
     })
     return env
 
-global_env = standard_env()
+global_env = standard_env()
+
+def eval(x: Exp, env=global_env) -> Exp:
+    'Evaluate an expression in an environment.'
+    if isinstance(x, Symbol):
+        return env[x]
+    elif isinstance(x, Number):
+        return x
+    elif x[0] == 'if':
+        (_,test,conseq,alt) = x
+        exp = ( conseq if eval(test,env) else alt)
+        return eval(exp, env)
+    elif x[0] == 'define':
+        (_,symbol, exp) = x
+        env[symbol] = eval(exp,env)
+    else:
+        proc = eval(x[0], env)
+        args = [eval(arg,env) for arg in x[1:]]
+        return proc(*args)
+    
+print(eval(parse(program)))
+
+    
+    

TypeScript/lisp.ts

@@ -1,47 +1,52 @@
 // Lispts: Scheme Interpreter in TypeScript
 
-const program = "(begin (define r 10) (* pi (* r r)))"
+const program = '(begin (define r 10) (* pi (* r r)))'
 
-// types
+//--------- types ------------
 type LSymbolType = 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 = LSymbolType | 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 = Map<string, any>;
+type Env = Map<string, any>
 
+//---------- utils -------------
 class LSymbol {
-  readonly value: string;
+  readonly value: string
 
   constructor(value: string) {
-    this.value = value;
+    this.value = value
   }
 
   toString(): string {
-    return this.value;
+    return this.value
   }
 }
 
-// utils
-const deepEqual = (a: any, b: any): boolean =>{
-  if(a=== b) return true
+const deepEqual = (a: any, b: any): boolean => {
+  if (a === b) return true
 
-  if(typeof a !== 'object'|| typeof b !== 'object' || a === null || b === null )
-  return false
+  if (
+    typeof a !== 'object' ||
+    typeof b !== 'object' ||
+    a === null ||
+    b === null
+  )
+    return false
 
   const keyA = Object.keys(a)
   const keyB = Object.keys(b)
 
-  if(keyA.length !== keyB.length) return false
+  if (keyA.length !== keyB.length) return false
 
-
-  for(const key of keyA){
-    if(!keyB.includes(key) || !deepEqual(a[key], b[key])) return false
+  for (const key of keyA) {
+    if (!keyB.includes(key) || !deepEqual(a[key], b[key])) return false
   }
-  
+
   return true
 }
 
+//---------- Parsing: parse, tokenize, and read_from_tokens ----------------
 /**
  * Read a Scheme expression from a string.
  */
@@ -61,9 +66,9 @@ const tokenize = (char: string): string[] =>
  * Numbers become numbers; every other token is a symbol(LSymbol).
  */
 const atom = (token: string): Atom =>
-  isNaN(Number(token)) ? token as LSymbolType : Number(token)
+  isNaN(Number(token)) ? (token as LSymbolType) : Number(token)
 
-  /**
+/**
  * Read an expression from a sequence of tokens
  */
 const readFromTokens = (tokens: string[]): Exp => {
@@ -85,7 +90,7 @@ const readFromTokens = (tokens: string[]): Exp => {
   }
 }
 
-// Environments
+// ---------------- Environments ------------------
 /**
  * An environment with some Scheme standard procedures
  */
@@ -104,26 +109,60 @@ const standardEnv = (): Env => {
   env.set('append', (a: any[], b: any[]) => a.concat(b))
   env.set('apply', (proc: Function, args: any[]) => proc(...args))
   env.set('begin', (...x: any) => x[x.length - 1])
-  env.set('car', (...x: any) => x[0])
-  env.set('cdr', (...x: any) => x.slice(1))
-  env.set('cons', (x: any, y: any) => [x, ...y])
+  env.set('car', (...x: any[]) => x[0])
+  env.set('cdr', (...x: any[]) => x.slice(1))
+  env.set('cos', Math.cos)
+  env.set('cons', (x: any, y: any[]) => [x, ...y])
   env.set('eq?', (a: any, b: any) => Object.is(a, b))
   env.set('equal?', (a: any, b: any) => deepEqual(a, b))
   env.set('expt', Math.pow)
   env.set('length', (x: any[]) => x.length)
   env.set('list', (...x: any[]) => Array.from(x))
   env.set('list?', (x: any) => Array.isArray(x))
-  env.set('map', Array.prototype.map)
+  env.set('map', (func: (value: any, index: number, array: any[]) => unknown, arr: any[]) => arr.map(func))
   env.set('max', Math.max)
   env.set('min', Math.min)
   env.set('not', (x: boolean) => !x)
   env.set('null?', (x: any[]) => x.length === 0)
   env.set('number?', (x: any) => typeof x === 'number')
   env.set('print', console.log)
+  env.set('pi', Math.PI)
   env.set('procedure?', (x: any) => typeof x === 'function')
   env.set('round', Math.round)
-  env.set('symbol?', (x: any) =>x instanceof LSymbol )
+  env.set('sin', Math.sin)
+  env.set('symbol?', (x: any) => x instanceof LSymbol)
   return env
 }
 
-const globalEnv = standardEnv()
+const globalEnv = standardEnv()
+
+/**
+ * Evaluate an expression in an environment.
+ */
+const evalScheme = (x: Exp, env = globalEnv): Exp => {
+  if (typeof x === 'string') {
+    // variable reference
+    return env.get(x) ?? new Error('Undefined symbol:' + x)
+  } else if (typeof x === 'number') {
+    return x
+  } else if (Array.isArray(x) && x[0] === 'if') {
+    const [_, test, consq, alt] = x
+    const exp = evalScheme(test, env) ? consq : alt
+    return evalScheme(exp, env)
+  } else if (Array.isArray(x) && x[0] === 'define') {
+    const [_, symbol, exp] = x
+    const value = evalScheme(exp, env)
+    env.set(symbol, value)
+    return value
+  } else {
+    const [op, ...args] = (x as List).map((e: Exp) => evalScheme(e, env))
+
+    if (typeof op === 'function') {
+      return (op as Function)(...args)
+    } else {
+      throw new Error(`${op} is not function`)
+    }
+  }
+}
+
+console.log(evalScheme(parse(program)))