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The scope of each declaration is the section of the program in which references to "p" resolve to that declaration. Each declaration represents a unique identifier "p". The symbol table must have some means of differentiating references to the different "p"s. A common data structure used to implement symbol tables is the hash table. The time ...
The most frequently used general-purpose implementation of an associative array is with a hash table: an array combined with a hash function that separates each key into a separate "bucket" of the array. The basic idea behind a hash table is that accessing an element of an array via its index is a simple, constant-time operation.
A symbol in Lisp is unique in a namespace (or package in Common Lisp). Symbols can be tested for equality with the function EQ. Lisp programs can generate new symbols at runtime. When Lisp reads data that contains textual represented symbols, existing symbols are referenced. If a symbol is unknown, the Lisp reader creates a new symbol.
But that symbol table is remembered, rather than destroyed, and it remembers its higher level "parent" symbol table and so on. Thus when the compiler is later performing translations over the abstract syntax tree, for any given expression, it can fetch the symbol table representing that expression's environment and can resolve references to ...
The AST is used intensively during semantic analysis, where the compiler checks for correct usage of the elements of the program and the language. The compiler also generates symbol tables based on the AST during semantic analysis. A complete traversal of the tree allows verification of the correctness of the program.
In the SQUOZE encoding, identifiers in the symbol table were represented in a 50-character alphabet, allowing a 36-bit machine word to represent six alphanumeric characters plus two flag bits, thus saving two bits per six characters, [6] [1] because the six bits normally allocated for each character could store up to 64 states rather than only the 50 states needed to represent the 50 letters ...
When an object is created, a pointer to this table, called the virtual table pointer, vpointer or VPTR, is added as a hidden member of this object. As such, the compiler must also generate "hidden" code in the constructors of each class to initialize a new object's virtual table pointer to the address of its class's virtual method table.
The character between the address and the symbol (separated by spaces) is the type of a symbol. The nm utility program on Unix systems lists the symbols from object files. The System.map is directly related to it, in that this file is produced by nm on the whole kernel program – just like nm lists the symbols and their types for any small object programs.