feat: Support basic expression

lib/parser.mly

@@ -0,0 +1,51 @@
+/* lib/parser.mly */
+%{
+   open Ast
+%}
+
+%token <int> INT
+
+%token PLUS "+"
+%token MINUS "-"
+%token TIMES "*"
+%token DIVIDE "/"
+
+%token LPAREN "("
+%token RPAREN ")"
+
+%token SEMICOLON ";"
+
+%token EOF
+
+%left "+" "-"
+%left "*" "/"
+//%nonassoc UMINUS
+
+%start main
+%type <source_file> main
+
+%%
+
+main:
+  | statements EOF { SourceFile($1) }
+
+statements:
+  | statement ";" { [$1] }
+  | statement ";" statements { $1 :: $3 }
+
+statement:
+  | expression { ExpressionStatement($1) }
+
+expression:
+  | literal { $1 }
+  | binary_expression { $1 }
+  | "(" expression ")" { $2 }
+
+literal:
+  | INT { IntegerLiteral($1) }
+
+binary_expression:
+  | e1=expression PLUS e2=expression { BinaryExpression(Add, e1, e2) }
+  | e1=expression MINUS e2=expression { BinaryExpression(Substract, e1, e2) }
+  | e1=expression TIMES e2=expression { BinaryExpression(Multiply, e1, e2) }
+  | e1=expression DIVIDE e2=expression { BinaryExpression(Divide, e1, e2) }