fix: not declared errors in source native variant REPL

[shenyih0ng]

Fixes #1477

Description

When using the REPL with the Source Native variant, UndefinedVariable errors will be raised when trying to reference previously declared functions in the REPL.

This happens when a user first runs a program in the editor (via the "play" button) and subsequently tries to access the functions/variables in the REPL.

The Cause

UndefinedVariable Errors

The bug is due to the function and variable identifiers not being properly kept tracked of during the transpilation stage of a Source Native program.

Declared functions and variables in a program are not added to the context (in context.nativeStorage) when executing a program. Hence, upon accessing previously declared functions/variables, an UndefinedVariable error will be raised as those declarations have been lost.

The fix would be add those declarations during the transpilation stage of a Source Native program:

js-slang/src/transpiler/transpiler.ts

Lines 682 to 687 in bf698f1

	getFunctionDeclarationNamesInProgram(program).forEach(id =>
	context.nativeStorage.previousProgramsIdentifiers.add(id)
	)
	getGloballyDeclaredIdentifiers(program).forEach(id =>
	context.nativeStorage.previousProgramsIdentifiers.add(id)
	)

Why does f; not result in a UndefinedVariable error?

The bug is due to the use of getIdentifiersInProgram during the pre-evaluation stage of the FullJSRunner:

js-slang/src/runner/fullJSRunner.ts

Lines 73 to 75 in afcff0d

	getIdentifiersInProgram(preEvalProgram).forEach(id =>
	context.nativeStorage.previousProgramsIdentifiers.add(id)
	)

The snippet above adds all identifiers in the program, which includes identifiers of arguments in a function declaration, into the program context.

It turns out some of the arguments we have in our stdlib functions are named f:

js-slang/src/stdlib/list.prelude.ts

Lines 44 to 51 in bf698f1

	function $map(f, xs, acc) {
	return is_null(xs)
	? reverse(acc)
	: $map(f, tail(xs), pair(f(head(xs)), acc));
	}
	function map(f, xs) {
	return $map(f, xs, null);
	}

f works in Source Native 2-4 since the list is introduced in those chapters and not in Source Native 1.

The fix for this is the same for the error above. Instead of using getIdentifiersInProgram we specifically pick out function and variable declarations using getFunctionDeclarationNamesInProgram and getGloballyDeclaredIdentifiers

[martin-henz]

Yes, makes sense.

[martin-henz]

Looks good!