symbol-table

symbol-table

A data structure for tracking symbols in a compiler or interpreter.

var SymbolTable = require("symbol-table");

//create the root scope
var s0 = SymbolTable();

//define some symbols
s0.set("a", 1);
s0.set("b", 2);

//now enter a sub-scope that inherits s0
var s1 = s0.push();

//define/override symbols in the new scope
s1.set("b", 200);
s1.set("c", 300);

//s1 inherited "a"
s1.get("a");
//-> 1

//s1 changed "b"
s1.get("b");
//-> 200
//but s0 "b" was not touched
s0.get("b");
//-> 2

//s1 has "c", but s0 does not
s1.has("c");
//-> true
s0.has("c");
//-> false

API

s = SymbolTable()

Creates a new symbol table.

s.has(symbol)

Returns true if the symbol is in scope.

value = s.get(symbol)

Returns the value associated with that symbol in scope. Returns undefined if not found.

s.set(symbol, value)

Set the value associated with symbol. This can be anything you want. It can be another data structure if you need to store symbol values and type information for example.

s.unset(symbol)

Remove a symbol from a scope

s2 = s.push()

Return a new scope that inherits the current scope.

Stack

Create a stack of symbol tables/scopes where you always work with the current scope at the top of the stack. It has the same API as the symbol table except you push/pop the scope.

var SymbolTableStack = require("symbol-table/stack");

var s = SymbolTableStack();

s.set("a", 1);
s.push();

s.set("a", 2);
s.get("a");
//-> 2

s.pop();

s.get("a");
//-> 1

has, get, set, unset

These all work the same as the symbol table. However, it will always be the scope at the top of the stack.

table = s.push()

Creates a new table/scope and pushes it on top of the stack. It also returns the new table.

table = s.pop()

Pops the current table/scope off the stack.

i = s.height()

Get the stack height (initially it's 1)

i = s.getItsHeight(symbol)

What was the stack height when this symbol was set/defined? Returns undefined if the symbol is not found.

License

MIT