diff options
author | Eduardo Julian | 2017-04-15 22:03:36 -0400 |
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committer | Eduardo Julian | 2017-04-15 22:03:36 -0400 |
commit | 2b4d59eaa9f2827b7eeeed45e3c9de811b8f86a5 (patch) | |
tree | 697b3c24912e641e720af54c957118edfd73507b /new-luxc/source/luxc/parser.lux | |
parent | 4295ff3a08dae2d1a31284d752c2e955456d9a32 (diff) |
- Some refactorings.
- Added documentation for luxc/parser.
Diffstat (limited to '')
-rw-r--r-- | new-luxc/source/luxc/parser.lux | 346 |
1 files changed, 270 insertions, 76 deletions
diff --git a/new-luxc/source/luxc/parser.lux b/new-luxc/source/luxc/parser.lux index 25f9af46a..cac3cb862 100644 --- a/new-luxc/source/luxc/parser.lux +++ b/new-luxc/source/luxc/parser.lux @@ -1,9 +1,37 @@ +## This is the LuxC's parser. +## It takes the source code of a Lux file in raw text form and +## extracts the syntactic structure of the code from it. +## It only produces Lux AST nodes, and thus removes any white-space +## and comments while processing its inputs. + +## Another important aspect of the parser is that it keeps track of +## its position within the input data. +## That is, the parser takes into account the line and column +## information in the input text (it doesn't really touch the +## file-name aspect of the cursor, leaving it intact in whatever +## base-line cursor it is given). + +## This particular piece of functionality is not located in one +## function, but it is instead scattered throughout several parsers, +## since the logic for how to update the cursor varies, depending on +## what is being parsed, and the rules involved. + +## You will notice that several parsers have a "where" parameter, that +## tells them the cursor position prior to the parser being run. +## They are supposed to produce some parsed output, alongside an +## updated cursor pointing to the end position, after the parser was run. + +## Lux AST nodes/tokens are annotated with cursor meta-data +## (file-name, line, column) to keep track of their provenance and +## location, which is helpful for documentation and debugging. + (;module: lux (lux (control monad) (data [bool] [char] [text] + ["E" error #*] [number] (text ["l" lexer #+ Lexer Monad<Lexer> "l/" Monad<Lexer>] format) @@ -11,11 +39,21 @@ (coll [list "L/" Functor<List> Fold<List>] ["V" vector])))) +(def: white-space Text "\t\v \r\f") +(def: new-line "\n") + +## This is the parser for white-space. +## Whenever a new-line is encountered, the column gets reset to 0, and +## the line gets incremented. +## It operates recursively in order to produce the longest continuous +## chunk of white-space. (def: (space^ where) (-> Cursor (Lexer [Text Cursor])) (do Monad<Lexer> - [head (l;some' (l;one-of "\t\v \r\f"))] - (l;either (l;after (l;one-of "\n") + [head (l;some' (l;one-of white-space))] + ## New-lines must be handled as a separate case to ensure line + ## information is handled properly. + (l;either (l;after (l;one-of new-line) (do @ [[tail end] (space^ (|> where (update@ #;line n.inc) @@ -26,23 +64,33 @@ (|> where (update@ #;column (n.+ (text;size head))))])))) +## Single-line comments can start anywhere, but only go up to the +## next new-line. (def: (single-line-comment^ where) (-> Cursor (Lexer [Text Cursor])) - (l;enclosed ["##" "\n"] - (do Monad<Lexer> - [comment (l;some' (l;none-of "\n"))] - (wrap [comment - (|> where - (update@ #;line n.inc) - (set@ #;column +0))])))) + (do Monad<Lexer> + [_ (l;text "##") + comment (l;some' (l;none-of new-line)) + _ (l;text new-line)] + (wrap [comment + (|> where + (update@ #;line n.inc) + (set@ #;column +0))]))) +## This is just a helper parser to find text which doesn't run into +## any special character sequences for multi-line comments. (def: comment-bound^ (Lexer Text) ($_ l;either - (l;text "\n") + (l;text new-line) (l;text ")#") (l;text "#("))) +## Multi-line comments are bounded by #( these delimiters, #(and, they may +## also be nested)# )#. +## Multi-line comment syntax must be balanced. +## That is, any nested comment must have matched delimiters. +## Unbalanced comments ought to be rejected as invalid code. (def: (multi-line-comment^ where) (-> Cursor (Lexer [Text Cursor])) (do Monad<Lexer> @@ -51,21 +99,31 @@ where (|> where (update@ #;column (n.+ +2)))] ($_ l;either + ## These are normal chunks of commented text. (do @ [chunk (l;many' (l;not comment-bound^))] (recur (format comment chunk) (|> where (update@ #;column (n.+ (text;size chunk)))))) + ## This is a special rule to handle new-lines within + ## comments properly. (do @ - [_ (l;one-of "\n")] - (recur (format comment "\n") + [_ (l;text new-line)] + (recur (format comment new-line) (|> where (update@ #;line n.inc) (set@ #;column +0)))) + ## This is the rule for handling nested sub-comments. + ## Ultimately, the whole comment is just treated as text + ## (the comment must respect the syntax structure, but the + ## output produced is just a block of text). + ## That is why the sub-comment is covered in delimiters + ## and then appended to the rest of the comment text. (do @ [[sub-comment sub-where] (multi-line-comment^ where)] (recur (format comment "#(" sub-comment ")#") sub-where)) + ## Finally, this is the rule for closing the comment. (do @ [_ (l;text ")#")] (wrap [comment @@ -73,36 +131,53 @@ (update@ #;column (n.+ +2)))])) )))) +## This is the only parser that should be used directly by other +## parsers, since all comments must be treated as either being +## single-line or multi-line. +## That is, there is no syntactic rule prohibiting one type of comment +## from being used in any situation (alternatively, forcing one type +## of comment to be the only usable one). (def: (comment^ where) (-> Cursor (Lexer [Text Cursor])) (l;either (single-line-comment^ where) (multi-line-comment^ where))) -(def: (padding^ where) +## To simplify parsing, I remove any left-padding that an AST token +## may have prior to parsing the token itself. +## Left-padding is assumed to be either white-space or a comment. +## The cursor gets updated, but the padding gets ignored. +(def: (left-padding^ where) (-> Cursor (Lexer Cursor)) (l;either (do Monad<Lexer> [[comment where] (comment^ where)] - (padding^ where)) + (left-padding^ where)) (do Monad<Lexer> [[white-space where] (space^ where)] (wrap where)) )) +## Escaped character sequences follow the usual syntax of +## back-slash followed by a letter (e.g. \n). +## Unicode escapes are possible, with hexadecimal sequences between 1 +## and 4 characters long (e.g. \u12aB). +## Escaped characters may show up in Char and Text literals. (def: escaped-char^ (Lexer [Text Char]) (l;after (l;char #"\\") (do Monad<Lexer> [code l;any] (case code - #"t" (wrap ["\\t" #"\t"]) - #"v" (wrap ["\\v" #"\v"]) - #"b" (wrap ["\\b" #"\b"]) - #"n" (wrap ["\\n" #"\n"]) - #"r" (wrap ["\\r" #"\r"]) - #"f" (wrap ["\\f" #"\f"]) + ## Handle special cases. + #"t" (wrap ["\\t" #"\t"]) + #"v" (wrap ["\\v" #"\v"]) + #"b" (wrap ["\\b" #"\b"]) + #"n" (wrap ["\\n" #"\n"]) + #"r" (wrap ["\\r" #"\r"]) + #"f" (wrap ["\\f" #"\f"]) #"\"" (wrap ["\\\"" #"\""]) #"\\" (wrap ["\\\\" #"\\"]) + ## Handle unicode escapes. #"u" (do Monad<Lexer> [code (l;between' +1 +4 l;hex-digit)] @@ -117,6 +192,13 @@ _ (l;fail (format "Invalid escaping syntax: " (%c code))))))) +## A character can be either a normal glyph, or a escaped character. +## The reason why this parser returns both the Char and it's textual +## representation in the source-code, is for the sake of updating the +## cursor after parsing the char. +## A character only represents one glyph, but it's source-code +## representation may be multi-glyph (e.g. \u1234, \n), in which case, +## the text that was parsed needs to be counted to update the cursor. (def: raw-char^ (Lexer [Text Char]) (l;either (do Monad<Lexer> @@ -124,6 +206,9 @@ (wrap [(char;as-text char) char])) escaped-char^)) +## These are very simple parsers that just cut chunks of text in +## specific shapes and then use decoders already present in the +## standard library to actually produce the values from the literals. (do-template [<name> <tag> <lexer> <codec>] [(def: (<name> where) (-> Cursor (Lexer [AST Cursor])) @@ -141,13 +226,16 @@ [bool^ #;BoolS (l;either (l;text "true") (l;text "false")) bool;Codec<Text,Bool>] + [nat^ #;NatS (l;seq' (l;text "+") (l;many' l;digit)) number;Codec<Text,Nat>] + [int^ #;IntS (l;seq' (l;default "" (l;text "-")) (l;many' l;digit)) number;Codec<Text,Int>] + [real^ #;RealS ($_ l;seq' (l;default "" (l;text "-")) @@ -155,12 +243,15 @@ (l;text ".") (l;many' l;digit)) number;Codec<Text,Real>] + [deg^ #;DegS (l;seq' (l;text ".") (l;many' l;digit)) number;Codec<Text,Deg>] ) +## This parser doesn't delegate the work of producing the value to a +## codec, since the raw-char^ parser already takes care of that magic. (def: (char^ where) (-> Cursor (Lexer [AST Cursor])) (do Monad<Lexer> @@ -170,62 +261,98 @@ (|> where (update@ #;column (|>. ($_ n.+ +3 (text;size chunk)))))]))) +## This parser looks so complex because text in Lux can be multi-line +## and there are rules regarding how this is handled. (def: (text^ where) (-> Cursor (Lexer [AST Cursor])) (do Monad<Lexer> - [_ (l;text "\"") + [## Lux text "is delimited by double-quotes", as usual in most + ## programming languages. + _ (l;text "\"") + ## I must know what column the text body starts at (which is + ## always 1 column after the left-delimiting quote). + ## This is important because, when procesing subsequent lines, + ## they must all start at the same column, being left-padded with + ## as many spaces as necessary to be column-aligned. + ## This helps ensure that the formatting on the text in the + ## source-code matches the formatting of the Text value. #let [offset-column (n.inc (get@ #;column where))] [text-read where'] (: (Lexer [Text Cursor]) + ## I must keep track of how much of the + ## text body has been read, how far the + ## cursor has progressed, and whether I'm + ## processing a subsequent line, or just + ## processing normal text body. (loop [text-read "" where (|> where (update@ #;column n.inc)) - next-line-start? false] - (let [next-line (do @ - [_ (l;text "\n")] - (recur (format text-read "\n") + must-have-offset? false] + (l;either (if must-have-offset? + ## If I'm at the start of a + ## new line, I must ensure the + ## space-offset is at least + ## as great as the column of + ## the text's body's column, + ## to ensure they are aligned. + (do @ + [offset (l;many' (l;char #" ")) + #let [offset-size (text;size offset)]] + (if (n.>= offset-column offset-size) + ## Any extra offset + ## becomes part of the + ## text's body. + (recur (|> offset + (text;split offset-column) + (default (undefined)) + product;right + (format text-read)) + (|> where + (update@ #;column (n.+ offset-size))) + false) + (l;fail (format "Each line of a multi-line text must have an appropriate offset!\n" + "Expected: " (%i (nat-to-int offset-column)) " columns.\n" + " Actual: " (%i (nat-to-int offset-size)) " columns.\n")))) + ($_ l;either + ## Normal text characters. + (do @ + [normal (l;many' (l;none-of "\\\"\n"))] + (recur (format text-read normal) + (|> where + (update@ #;column (n.+ (text;size normal)))) + false)) + ## Must handle escaped + ## chars separately. + (do @ + [[chunk char] escaped-char^] + (recur (format text-read (char;as-text char)) (|> where - (update@ #;line n.inc) - (set@ #;column +0)) - true))] - (if next-line-start? - (l;either next-line - (do @ - [offset (l;many' (l;char #" ")) - #let [offset-size (text;size offset)]] - (if (n.>= offset-column offset-size) - (recur (|> offset - (text;split offset-column) - (default (undefined)) - product;right - (format text-read)) + (update@ #;column (n.+ (text;size chunk)))) + false)) + ## The text ends when it + ## reaches the right-delimiter. + (do @ + [_ (l;text "\"")] + (wrap [text-read (|> where - (update@ #;column (n.+ offset-size))) - false) - (l;fail (format "Each line of a multi-line text must have an appropriate offset!\n" - "Expected: " (%i (nat-to-int offset-column)) " columns.\n" - " Actual: " (%i (nat-to-int offset-size)) " columns.\n"))))) - ($_ l;either - (do @ - [normal (l;many' (l;none-of "\\\"\n"))] - (recur (format text-read normal) - (|> where - (update@ #;column (n.+ (text;size normal)))) - false)) - (do @ - [[chunk char] escaped-char^] - (recur (format text-read (char;as-text char)) - (|> where - (update@ #;column (n.+ (text;size chunk)))) - false)) - next-line - (do @ - [_ (l;text "\"")] - (wrap [text-read - (|> where - (update@ #;column n.inc))])))))))] + (update@ #;column n.inc))])))) + ## If a new-line is + ## encountered, it gets + ## appended to the value and + ## the loop is alerted that the + ## next line must have an offset. + (do @ + [_ (l;text new-line)] + (recur (format text-read new-line) + (|> where + (update@ #;line n.inc) + (set@ #;column +0)) + true)))))] (wrap [[where (#;TextS text-read)] where']))) +## Form and tuple syntax is mostly the same, differing only in the +## delimiters involved. +## They may have an arbitrary number of arbitrary AST nodes as elements. (do-template [<name> <tag> <open> <close>] [(def: (<name> where ast^) (-> Cursor @@ -237,11 +364,16 @@ V;empty) where where] (l;either (do @ - [[elem where'] (ast^ where)] + [## Must update the cursor as I + ## go along, to keep things accurate. + [elem where'] (ast^ where)] (recur (V;add elem elems) where')) (do @ - [where' (padding^ where) + [## Must take into account any + ## padding present before the + ## end-delimiter. + where' (left-padding^ where) _ (l;text <close>)] (wrap [(V;to-list elems) (|> where' @@ -253,6 +385,15 @@ [tuple^ #;TupleS "[" "]"] ) +## Records are almost (syntactically) the same as forms and tuples, +## with the exception that their elements must come in pairs (as in +## key-value pairs). +## Semantically, though, records and tuples are just 2 different +## representations for the same thing (a tuple). +## In normal Lux syntax, the key position in the pair will be a tag +## AST node, however, record AST nodes allow any AST node to occupy +## this position, since it may be useful when processing AST syntax in +## macros. (def: (record^ where ast^) (-> Cursor (-> Cursor (Lexer [AST Cursor])) @@ -263,12 +404,12 @@ V;empty) where where] (l;either (do @ - [[key where] (ast^ where) - [val where'] (ast^ where)] + [[key where'] (ast^ where) + [val where'] (ast^ where')] (recur (V;add [key val] elems) where')) (do @ - [where' (padding^ where) + [where' (left-padding^ where) _ (l;text "}")] (wrap [(V;to-list elems) (|> where' @@ -276,12 +417,34 @@ (wrap [[where (#;RecordS elems)] where']))) +## The parts of an identifier are separated by a single mark. +## E.g. module;name. +## Only one such mark may be used in an identifier, since there +## can only be 2 parts to an identifier (the module [before the +## mark], and the name [after the mark]). +## There are also some extra rules regarding identifier syntax, +## encoded on the parser. +(def: identifier-separator Text ";") + +## A Lux identifier is a pair of chunks of text, where the first-part +## refers to the module that gives context to the identifier, and the +## second part corresponds to the name of the identifier itself. +## The module part may be absent (by being the empty text ""), but the +## name part must always be present. +## The rules for which characters you may use are specified in terms +## of which characters you must avoid (to keep things as open-ended as +## possible). +## In particular, no white-space can be used, and neither can other +## characters which are already used by Lux as delimiters for other +## AST nodes (thereby reducing ambiguity while parsing). +## Additionally, the first character in an identifier's part cannot be +## a digit, to avoid confusion with regards to numbers. (def: ident-part^ (Lexer Text) (do Monad<Lexer> [#let [digits "0123456789" - delimiters "()[]{}#;\"" - space "\t\v \n\r\f" + delimiters (format "()[]{}#\"" identifier-separator) + space (format white-space new-line) head-lexer (l;none-of (format digits delimiters space)) tail-lexer (l;some' (l;none-of (format delimiters space)))] head head-lexer @@ -292,19 +455,39 @@ (def: ident^ (Lexer [Ident Nat]) ($_ l;either + ## When an identifier starts with 2 marks, it's module is + ## taken to be the current-module being compiled at the moment. + ## This can be useful when mentioning identifiers and tags + ## inside quoted/templated code in macros. (do Monad<Lexer> - [_ (l;text ";;") + [#let [current-module-mark (format identifier-separator identifier-separator)] + _ (l;text current-module-mark) def-name ident-part^] - (l;fail "Cannot handle ;; syntax for identifiers.")) + (l;fail (format "Cannot handle " current-module-mark " syntax for identifiers."))) + ## If the identifier is prefixed by the mark, but no module + ## part, the module is assumed to be "lux" (otherwise known as + ## the 'prelude'). + ## This makes it easy to refer to definitions in that module, + ## since it is the most fundamental module in the entire + ## standard library. (do Monad<Lexer> - [_ (l;text ";") + [_ (l;text identifier-separator) def-name ident-part^] (wrap [["lux" def-name] (n.inc (text;size def-name))])) + ## Not all identifiers must be specified with a module part. + ## If that part is not provided, the identifier will be created + ## with the empty "" text as the module. + ## During program analysis, such identifiers tend to be treated + ## as if their context is the current-module, but this only + ## applies to identifiers for tags and module definitions. + ## Function arguments and local-variables may not be referred-to + ## using identifiers with module parts, so being able to specify + ## identifiers with empty modules helps with those use-cases. (do Monad<Lexer> [first-part ident-part^] (l;either (do @ - [_ (l;char #";") + [_ (l;text identifier-separator) second-part ident-part^] (wrap [[first-part second-part] ($_ n.+ @@ -314,6 +497,13 @@ (wrap [["" first-part] (text;size first-part)]))))) +## The only (syntactic) difference between a symbol and a tag (both +## being identifiers), is that tags must be prefixed with a hash-sign +## (i.e. #). +## Semantically, though, they are very different, with symbols being +## used to refer to module definitions and local variables, while tags +## provide the compiler with information related to data-structure +## construction and de-structuring (during pattern-matching). (do-template [<name> <tag> <lexer> <extra>] [(def: (<name> where) (-> Cursor (Lexer [AST Cursor])) @@ -327,10 +517,10 @@ [tag^ #;TagS (l;after (l;char #"#") ident^) +1] ) -(def: #export (ast^ where) +(def: (ast^ where) (-> Cursor (Lexer [AST Cursor])) (do Monad<Lexer> - [where (padding^ where)] + [where (left-padding^ where)] ($_ l;either (form^ where ast^) (tuple^ where ast^) @@ -345,3 +535,7 @@ (char^ where) (text^ where) ))) + +(def: #export (parse where code) + (-> Cursor Text (Error [Text AST Cursor])) + (l;run' code (ast^ where))) |