Agda-2.2.6: A dependently typed functional programming language and proof assistant




The lexer is generated by Alex ( and is an adaptation of GHC's lexer. The main lexing function lexer is called by the Agda.Syntax.Parser.Parser to get the next token from the input.


The main function

lexer :: (Token -> Parser a) -> Parser aSource

Return the next token. This is the function used by Happy in the parser.

lexer k = lexToken >>= k

Lex states

normal :: LexStateSource

This is the initial state for parsing a regular, non-literate file.

literate :: LexStateSource

This is the initial state for parsing a literate file. Code blocks should be enclosed in \begin{code} \end{code} pairs.

layout :: LexStateSource

The layout state. Entered when we see a layout keyword (withLayout) and exited either when seeing an open brace (openBrace) or at the next token (newLayoutContext).

Update: we don't use braces for layout anymore.

empty_layout :: LexStateSource

We enter this state from newLayoutContext when the token following a layout keyword is to the left of (or at the same column as) the current layout context. Example:

 data Empty : Set where
 foo : Empty -> Nat

Here the second line is not part of the where clause since it is has the same indentation as the data definition. What we have to do is insert an empty layout block {} after the where. The only thing that can happen in this state is that emptyLayout is executed, generating the closing brace. The open brace is generated when entering by newLayoutContext.

bol :: LexStateSource

This state is entered at the beginning of each line. You can't lex anything in this state, and to exit you have to check the layout rule. Done with offsideRule.

imp_dir :: LexStateSource

This state can only be entered by the parser. In this state you can only lex the keywords using, hiding, renaming and to. Moreover they are only keywords in this particular state. The lexer will never enter this state by itself, that has to be done in the parser.

Alex generated functions

alexScanUser :: ([LexState], ParseFlags) -> AlexInput -> Int -> AlexReturn (LexAction Token)Source

This is the main lexing function generated by Alex.