git @ Cat's Eye Technologies Castile / 6d24f81
Remove a little weirdness from the language. catseye 12 years ago
2 changed file(s) with 10 addition(s) and 36 deletion(s). Raw diff Collapse all Expand all
+2
-24
README.markdown less more
9393 Grammar
9494 -------
9595
96 The grammar is a little weird at points (especially the VarRef production,
97 which includes the possibility of assignment, even though that can really
98 only happen in a Stmt.)
99
10096 Program ::= {Defn [";"]}.
10197 Defn ::= "fun" ident "(" [Arg {"," Arg}] ")" Body
10298 | "struct" ident "{" {ident ":" TExpr [";"]} "}"
105101 Body ::= "{" {VarDecl [";"]} {Stmt [";"]} "}".
106102 VarDecl ::= "var" ident "=" Expr0.
107103 Stmt ::= "while" Expr0 Block
108 | "typecase" VarRef "is" TExpr0 Block
104 | "typecase" ident "is" TExpr0 Block
109105 | "do" Expr0
110106 | "return" Expr0
111107 | If
121117 | "(" Expr0 ")"
122118 | "not" Expr1
123119 | Literal
124 | VarRef.
125 VarRef ::= ident ["=" Expr0].
120 | ident ["=" Expr0].
126121 Literal ::= strlit
127122 | ["-"] intlit
128123 | "true" | "false" | "null"
10841079 | }
10851080 = nothing there
10861081
1087 This is a very strange case in the language. Thankfully, assignment
1088 typechecks as void, without any automatic promotion to the union type...
1089
1090 | fun foo(b: integer|void) {
1091 | var a = b;
1092 | typecase a is integer {
1093 | print("yes it's an integer");
1094 | }
1095 | typecase a = 7 as integer|void is void {
1096 | print("yes it's void too");
1097 | }
1098 | }
1099 | main = fun() {
1100 | foo(7 as integer|void)
1101 | }
1102 ? void not a union
1103
11041082 ### Struct Types + Union Types ###
11051083
11061084 Union types may be used to make fields of a struct "nullable", so that
+8
-12
src/castile/parser.py less more
251251 b = self.block()
252252 return AST('While', [t, b])
253253 elif self.consume('typecase'):
254 e = self.var_ref()
254 id = self.expect_type('identifier')
255 e = AST('VarRef', value=id)
255256 self.expect('is')
256257 te = self.texpr0()
257258 b = self.block()
360361 self.expect(')')
361362 return e
362363 else:
363 return self.var_ref()
364
365 def var_ref(self):
366 # Note: this production includes the possibility of assignment
367 # therefore slightly weird things can occur in the grammar
368 id = self.expect_type('identifier')
369 ast = AST('VarRef', value=id)
370 if self.consume('='):
371 e = self.expr0()
372 ast = AST('Assignment', [ast, e])
373 return ast
364 id = self.expect_type('identifier')
365 ast = AST('VarRef', value=id)
366 if self.consume('='):
367 e = self.expr0()
368 ast = AST('Assignment', [ast, e])
369 return ast
374370
375371 def literal(self):
376372 if self.on_type('string literal'):