diff --git a/CHANGELOG.md b/CHANGELOG.md --- a/CHANGELOG.md +++ b/CHANGELOG.md @@ -1,3 +1,10 @@ +* 0.1.5 (12 March 2022) + + - Syntax errors in function definitions now result in much more + helpful error messages. Before, it would just complain about + something being wrong with the '=' sign. + ([#346](https://github.com/disco-lang/disco/issues/346)) + * 0.1.4 (10 March 2022) - New features or syntax diff --git a/disco.cabal b/disco.cabal --- a/disco.cabal +++ b/disco.cabal @@ -1,6 +1,6 @@ cabal-version: 2.4 name: disco -version: 0.1.4 +version: 0.1.5 synopsis: Functional programming language for teaching discrete math. description: Disco is a simple functional programming language for use in teaching discrete math. Its syntax is designed to be close @@ -98,6 +98,8 @@ test/error-numpatterns/expected test/error-numpatterns/input test/error-numpatterns/numpatterns.disco + test/error-parse-RHS/expected + test/error-parse-RHS/input test/error-pattype/expected test/error-pattype/input test/error-polyrec/expected @@ -109,6 +111,8 @@ test/error-tyargs/error-tyargs.disco test/error-tyargs/expected test/error-tyargs/input + test/error-unbound/expected + test/error-unbound/input test/error-unboundtyvar/expected test/error-unboundtyvar/input test/error-unboundtyvar/unboundtyvar.disco @@ -309,6 +313,8 @@ test/syntax-types/input test/types-192/expected test/types-192/input + test/types-306/expected + test/types-306/input test/types-bind/expected test/types-bind/input test/types-char-string/expected diff --git a/src/Disco/Parser.hs b/src/Disco/Parser.hs --- a/src/Disco/Parser.hs +++ b/src/Disco/Parser.hs @@ -461,9 +461,26 @@ parseTopLevel :: Parser TopLevel parseTopLevel = L.nonIndented sc $ TLDoc <$> parseDocThing - <|> TLDecl <$> try parseDecl + <|> TLDecl <$> parseDecl -- See Note [Parsing definitions and top-level expressions] <|> TLExpr <$> thenIndented parseTerm + -- ~~~~ Note [Parsing definitions and top-level expressions] + -- + -- The beginning of a definition might look the same as an + -- expression. e.g. is f(x,y) the start of a definition of f, or an + -- expression with a function call? We used to therefore wrap + -- 'parseDecl' in 'try'. The problem is that if a definition has a + -- syntax error on the RHS, it would fail, backtrack, then try + -- parsing a top-level expression and fail when it got to the = + -- sign, giving an uninformative parse error message. + -- See https://github.com/disco-lang/disco/issues/346. + -- + -- The solution is that we now do more careful backtracking within + -- parseDecl itself: when parsing a definition, we only backtrack if + -- we don't get a complete LHS + '=' sign; once we start parsing the + -- RHS of a definition we no longer backtrack, since it can't + -- possibly be a valid top-level expression. + -- | Parse a documentation item: either a group of lines beginning -- with @|||@ (text documentation), or a group beginning with @!!!@ -- (checked examples/properties). @@ -507,10 +524,15 @@ -- | Parse a definition of the form @x pat1 .. patn = t@. parseDefn :: Parser TermDefn parseDefn = label "definition" $ - TermDefn - <$> ident - <*> indented ((:[]) <$> (bind <$> many parseAtomicPattern <*> (symbol "=" *> parseTerm))) + (\(x, ps) body -> TermDefn x [bind ps body]) + -- Only backtrack if we don't get a complete 'LHS ='. Once we see + -- an = sign, commit to parsing a definition, because it can't be a + -- valid standalone expression anymore. If the RHS fails, we don't + -- want to backtrack, we just want to display the parse error. + <$> try ((,) <$> ident <*> indented (many parseAtomicPattern) <* reservedOp "=") + <*> indented parseTerm + -- | Parse the definition of a user-defined algebraic data type. parseTyDefn :: Parser TypeDefn parseTyDefn = label "type defintion" $ do @@ -518,7 +540,7 @@ indented $ do name <- parseTyDef args <- fromMaybe [] <$> optional (parens $ parseTyVarName `sepBy1` comma) - _ <- symbol "=" + _ <- reservedOp "=" TypeDefn name args <$> parseType -- | Parse the entire input as a term (with leading whitespace and diff --git a/test/error-parse-RHS/expected b/test/error-parse-RHS/expected new file mode 100644 --- /dev/null +++ b/test/error-parse-RHS/expected @@ -0,0 +1,14 @@ +1:11: + | +1 | f(x) = x + + | ^ +unexpected end of input +expecting expression or operator + +1:18: + | +1 | g(x) = {? 5 if x =< 5, 6 otherwise ?} + | ^^ +unexpected "=<" +expecting "?}", "if", "let", "when", ',', expression, operator, or type annotation + diff --git a/test/error-parse-RHS/input b/test/error-parse-RHS/input new file mode 100644 --- /dev/null +++ b/test/error-parse-RHS/input @@ -0,0 +1,5 @@ +f : N -> N +f(x) = x + + +g : N -> N +g(x) = {? 5 if x =< 5, 6 otherwise ?} diff --git a/test/error-unbound/expected b/test/error-unbound/expected new file mode 100644 --- /dev/null +++ b/test/error-unbound/expected @@ -0,0 +1,1 @@ +Error: encountered undefined name REPL.even. Maybe you haven't defined it yet? diff --git a/test/error-unbound/input b/test/error-unbound/input new file mode 100644 --- /dev/null +++ b/test/error-unbound/input @@ -0,0 +1,2 @@ +even : Z -> Bool +even(2) diff --git a/test/types-306/expected b/test/types-306/expected new file mode 100644 --- /dev/null +++ b/test/types-306/expected @@ -0,0 +1,13 @@ +Error: the shape of two types does not match. +https://disco-lang.readthedocs.io/en/latest/reference/shape-mismatch.html +Error: the shape of two types does not match. +https://disco-lang.readthedocs.io/en/latest/reference/shape-mismatch.html +Error: values of type Bool → Bool cannot be compared. +https://disco-lang.readthedocs.io/en/latest/reference/not-qual.html +Error: values of type a5 → a6 cannot be compared. +https://disco-lang.readthedocs.io/en/latest/reference/not-qual.html +Error: the shape of two types does not match. +https://disco-lang.readthedocs.io/en/latest/reference/shape-mismatch.html +Error: the shape of two types does not match. +https://disco-lang.readthedocs.io/en/latest/reference/shape-mismatch.html +{} diff --git a/test/types-306/input b/test/types-306/input new file mode 100644 --- /dev/null +++ b/test/types-306/input @@ -0,0 +1,7 @@ +set [\x.x : Bool -> Bool, \x. not x] +{\x.x : Bool -> Bool, \x. not x} +{\x.x, \x. not x} : Set (Bool -> Bool) +{\x.x, \x. not x} +bag [\x.x : Bool -> Bool, \x. not x] +[\x.x : Bool -> Bool, \x. not x] +{} : Set (Bool -> Bool)