RepTIDE

I drafted this post back in December. I have since been distracted with “real work”, so I’ve never gotten back to it. At this point, I can’t remember what I was going to change or add to it, so I’ll just post it as-is.

I’ve been exploring the B programming language. I’ve had a casual interest in this for years and have only recently dug into it a little deeper. I created the following comparison to C for myself and anyone else who may be interested.

What’s different compared to C?

• No preprocessor or associated directives (no symbolic constants or macros).
• No explicit types or typedef keyword; all variables have “word” type, similar to the int type in C. B does not have array types as in C, just pointers to vectors.
• No type qualifiers or const or volatile keywords.
• No floating point support.
• auto keyword used to declare automatic (local) variables.
• extrn keyword instead of extern keyword.
• No static keyword in earliest versions (though Dennis Ritchie’s C History paper seems to indicate that it may have been added later).
• No sizeof operator.
• No function prototypes; must use extrn to declare functions before use.
• Identifiers are restricted to 7 characters and may contain the backspace character.
• Variable initializers do not include the equals sign. For example: auto x 1 declares an automatic variable x with the initial value 1.
• No hexadecimal constants.
• No structs, unions, or associated operators (. and ->).
• No enums.
• No do or for loop constructs.
• No continue, or default statements.
• No comma operator.
• No logical operators (&& and ||); must use bit-wise expressions.
• Assignment operators have the form =op instead of op= (as in early C prior to 1976).
• Relational assignment operators not found in C: ===, =!=, =<, =<=, =>, =>=.
• Thompson’s original manual did not include bit-wise exclusive OR operator (^), bit-wise not operator (~), or break statement (MH-TSS reference includes these).
• Escape character is * instead of \. For example, *n is the newline character.
• Additional escape sequences:
  • *(  {
  • *)  }
  • *e  EOT
• No equivalents to \a, \b, \f, \r, \v, \?, or octal/hexadecimal escape sequences.
• B strings are terminated with *e (ASCII EOT) rather than *0 (ASCII NUL).
• Controlling expressions for switch statements do not require parentheses.
• Parentheses are required for return statements when a value is returned. For example: return (x)
• Compound statements consisting of only a single statement preceded by variable declarations and/or label definitions need not be surrounded by braces in function definitions or if/while/switch constructs.

  Example 1: Read a character from stdin if cond is true.

  if (cond)
    auto unused;
    extrn read;
    read(0, &unused, 1);
  

  Example 2: Definition for a function g, which returns its parameter, f.

  g(f)
    return (f);

What’s similar?

• Expression structure, operators, and operator precedence, except as mentioned above.
• if/else, goto, switch, while, and return statements, aside from the differences mentioned above.
• Everything else not mentioned above.

References:

• Users’ Reference to B, Ken Thompson
• The Programming Language B, S. C. Johnson & B. W. Kernighan, Technical Report CS TR 8, Bell Labs (January 1973)
• The Development of the C Language, Dennis M. Ritchie.

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