The straightline programming language

Straightline is a micro programming language used in the book series Modern Compiler Implementation by Andrew Appel.

Grammar

• The syntax of the language is given by a context free grammar.
• Only the production rules are explicitly given.
• The sets of terminals and non-terminals are obtained from the rules.
• The initial symbol is the non-terminal on the left side of the first production rule.

Production rules

Stm → Stm ; Stm
Stm → id := Exp
Stm → print ( ExpList )
Exp → id
Exp → num
Exp → Exp Binop Exp
Exp → ( Stm , Exp )
ExpList → Exp
ExpList → Exp , ExpList
Binop → +
Binop → -
Binop → *
Binop → /

Operator Precedence and Associativity

In order to resolve possible conflicts during syntactic analysis, the following relation of operator precedence and associativity, in descending order, should be observed:

operators	associativity
* /	left
+ -	left
:=	right

Lexical symbols

• Spaces, newlines, and tabulators are white spaces.
• Comments starts with # and extends to the end of the line.
• A numerical literal is a sequence of one or more digits.
• An identifier is a sequence of one or more letters, digits and underscores, beginning with a letter, that is not a keyword.
• The keywords are: print.
• The operators are: :=, +, -, * and /.
• The special symbols are: ,, ;, ( and ).

Example

a := 5 + 3;
b := ( print(a, a-1), 10*a );
print(b)