Mx-Compiler-for-Course

This is a Compiler of Mx*(a toy language designed for tutoring) for ACM class, Shanghai Jiao Tong University.

Assignment Homepage

Frontend(Semantic Check)

Working Process

graph TD;

A[MxStar.g4] -->|Antlr4| B[Lexer&Parser];

B --> |parser tree|C["ASTBuilder"];

C -->|"Abstract Semantic Tree(AST)"| D[SemanticChecker]

D --> |Semantic Error| E[ExceptionCatcher]

B --> |Syntax Error| E

D --> |Pass Semantic Check| F[Codegen]

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Design of g4

Regular Expression

• | color|colour matches both color and colour
• * $A^* = {empty, A, AA, AAA, ...}$
• + $A^+ = {A, AA, AAA, ...}$

Lexer

only list the tricky part.

Identifier: [a-zA-Z][a-zA-Z_0-9]*

ESC : '\\"' | '\\\\' (to handle escape character)

StringConst : '"' (ESC | .)*? '"' (. means anything)

LineComment : '//' .*? '\r'? '\n' -> skip (comment should be aborted)

BlockComment : '/*' .*? '*/' -> skip

EndFileComment : '//' ~[\r\n]* -> skip (~[\r\n] means anything but \r and \n) (A nasty case. It happens when programmer write a line comment at of and of file. Then there is no \r or \n to mark that the line comment has come to an end.)

WhiteSpace: [ \t] -> skip

NewLine: ('\r\n' | '\n') -> skip

Parser

Semantic Check

Details that are easily ignored

• ++a can be recognized as a left value but a++ can't

• null can be assigned to array or class

• Variable is not available for back reference in global scope, but function and class can.

• Variable is available for back reference in class scope. (So I add all variable registries into class scope when AST building)

• int x = x + 1 is a semantic error. You should add registry of x at the end of variable define, not beginning.

• Variable, function and class can't share a same name at one scope.

• int [] [] graph = new int [][4] is a semantic error. The assignment of 2-D array should follow the order from the first dimension.