Lazy lists support for lazy source 2 (source-academy#564)

* added option for lazy evaluation to interpreter

* tests for lazy evaluation

* finished transpiler

* additional test case

* updated REPL to have nice command line args

* updated REPL to have nice command line args

* added html test reporter

* fixed function printing bug in REPL

* formatting

* fixed REPL printing bug for null and undefined

* changed REPL bug fix

* changed REPL bug fix

* implement lazy pairs

* add lazy pairs

* add tests for lists, fix bugs for lazy lists

* previous tests fixes

* remove console.log calls

* minor style fix for lazy context creation

* untracked coverage

* formatting

* Updated last references to evaluationMethod

Co-authored-by: Ian Duncan <[email protected]>

.gitignore

@@ -4,6 +4,7 @@ node_modules
 *.map
 dist/
 .idea/
+coverage/
 
 # emacs backup files
 *~

package.json

@@ -91,7 +91,7 @@
       "/src/typings/",
       "/src/utils/testing.ts"
     ],
-    "reporters": [
+      "reporters": [
       "default",
       [
         "./node_modules/jest-html-reporter",

src/createContext.ts

@@ -13,7 +13,15 @@ import { streamPrelude } from './stdlib/stream.prelude'
 import { Context, CustomBuiltIns, Value, Variant } from './types'
 import * as operators from './utils/operators'
 import { stringify } from './utils/stringify'
-
+import { lazyListPrelude } from './stdlib/lazyList.prelude'
+export class LazyBuiltIn {
+  func: (...arg0: any) => any
+  evaluateArgs: boolean
+  constructor(func: (...arg0: any) => any, evaluateArgs: boolean) {
+    this.func = func
+    this.evaluateArgs = evaluateArgs
+  }
+}
 const createEmptyRuntime = () => ({
   break: false,
   debuggerOn: true,
@@ -103,6 +111,12 @@ export const defineBuiltin = (context: Context, name: string, value: Value) => {
     wrapped.toString = () => repr
 
     defineSymbol(context, funName, wrapped)
+  } else if (value instanceof LazyBuiltIn) {
+    const wrapped = (...args: any) => value.func(...args)
+    const funName = name.split('(')[0].trim()
+    const repr = `function ${name} {\n\t[implementation hidden]\n}`
+    wrapped.toString = () => repr
+    defineSymbol(context, funName, new LazyBuiltIn(wrapped, value.evaluateArgs))
   } else {
     defineSymbol(context, name, value)
   }
@@ -154,13 +168,24 @@ export const importBuiltins = (context: Context, externalBuiltIns: CustomBuiltIn
 
   if (context.chapter >= 2) {
     // List library
-    defineBuiltin(context, 'pair(left, right)', list.pair)
-    defineBuiltin(context, 'is_pair(val)', list.is_pair)
-    defineBuiltin(context, 'head(xs)', list.head)
-    defineBuiltin(context, 'tail(xs)', list.tail)
-    defineBuiltin(context, 'is_null(val)', list.is_null)
-    defineBuiltin(context, 'list(...values)', list.list)
-    defineBuiltin(context, 'draw_data(xs)', visualiseList)
+
+    if (context.variant === 'lazy') {
+      defineBuiltin(context, 'pair(left, right)', new LazyBuiltIn(list.pair, false))
+      defineBuiltin(context, 'list(...values)', new LazyBuiltIn(list.list, false))
+      defineBuiltin(context, 'is_pair(val)', new LazyBuiltIn(list.is_pair, true))
+      defineBuiltin(context, 'head(xs)', new LazyBuiltIn(list.head, true))
+      defineBuiltin(context, 'tail(xs)', new LazyBuiltIn(list.tail, true))
+      defineBuiltin(context, 'is_null(val)', new LazyBuiltIn(list.is_null, true))
+      defineBuiltin(context, 'draw_data(xs)', new LazyBuiltIn(visualiseList, true))
+    } else {
+      defineBuiltin(context, 'pair(left, right)', list.pair)
+      defineBuiltin(context, 'is_pair(val)', list.is_pair)
+      defineBuiltin(context, 'head(xs)', list.head)
+      defineBuiltin(context, 'tail(xs)', list.tail)
+      defineBuiltin(context, 'is_null(val)', list.is_null)
+      defineBuiltin(context, 'list(...values)', list.list)
+      defineBuiltin(context, 'draw_data(xs)', visualiseList)
+    }
   }
 
   if (context.chapter >= 3) {
@@ -202,7 +227,7 @@ export const importBuiltins = (context: Context, externalBuiltIns: CustomBuiltIn
 function importPrelude(context: Context) {
   let prelude = ''
   if (context.chapter >= 2) {
-    prelude += listPrelude
+    prelude += context.variant === 'lazy' ? lazyListPrelude : listPrelude
   }
   if (context.chapter >= 3) {
     prelude += streamPrelude

src/interpreter/interpreter.ts

@@ -9,6 +9,7 @@ import { conditionalExpression, literal, primitive } from '../utils/astCreator'
 import { evaluateBinaryExpression, evaluateUnaryExpression } from '../utils/operators'
 import * as rttc from '../utils/rttc'
 import Closure from './closure'
+import { LazyBuiltIn } from '../createContext'
 import { loadIIFEModule } from '../modules/moduleLoader'
 
 class BreakValue {}
@@ -662,6 +663,33 @@ export function* apply(
         // No Return Value, set it as undefined
         result = new ReturnValue(undefined)
       }
+    } else if (fun instanceof LazyBuiltIn) {
+      try {
+        let finalArgs = args
+        if (fun.evaluateArgs) {
+          finalArgs = []
+          for (const arg of args) {
+            finalArgs.push(yield* forceIt(arg, context))
+          }
+        }
+        result = fun.func.apply(thisContext, finalArgs)
+        break
+      } catch (e) {
+        // Recover from exception
+        context.runtime.environments = context.runtime.environments.slice(
+          -context.numberOfOuterEnvironments
+        )
+
+        const loc = node ? node.loc! : constants.UNKNOWN_LOCATION
+        if (!(e instanceof RuntimeSourceError || e instanceof errors.ExceptionError)) {
+          // The error could've arisen when the builtin called a source function which errored.
+          // If the cause was a source error, we don't want to include the error.
+          // However if the error came from the builtin itself, we need to handle it.
+          return handleRuntimeError(context, new errors.ExceptionError(e, loc))
+        }
+        result = undefined
+        throw e
+      }
     } else if (typeof fun === 'function') {
       try {
         const forcedArgs = []

src/repl/repl.ts

@@ -14,7 +14,7 @@ function startRepl(
   prelude = ''
 ) {
   // use defaults for everything
-  const context = createContext(chapter)
+  const context = createContext(chapter, undefined, undefined, undefined)
   const options: Partial<IOptions> = {
     scheduler: 'preemptive',
     executionMethod,