package pratter
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sha512=89fc9d0645e55dda7201a2cb47fe7bee774db92892c528efcbec179f270563088b1fab1d8d25ebca97b389947c2741f7a05127996cd1a4e3c7fe726be45ab835
Description
Pratter is a library that provides a parser that transforms streams of terms to applied terms. Terms may contain infix or prefix operators and native applications. The parser is based on the Pratt parsing algorithm and extended to handle term application and non associative operators.
Published: 23 Jun 2022
README
Pratter: A parser for terms with operators and applications
Pratter is a library that provides a parser that transforms streams of terms to applied terms. Terms may contain infix, prefix or postfix operators and applications. The parser is an extension of the Pratt parsing algorithm.
Examples can be seen in tests inside the t/
folder.
Example: simple terms
Terms are made of symbols and applications and some symbol can be declared to be operators.
Start by defining the terms,
type term = Appl of term * term  Symb of string
and the data structure that maps symbols identifiers to operators properties,
type table = {
prefix : (string * Pratter.priority) list
; infix : (string * (Pratter.priority * Pratter.associativity)) list
; postfix : (string * Pratter.priority) list
}
Next, define a module to pack these two types, and two functions:
get
that is able to retrieve the properties of a symbol if it is declared as an operator,make_appl
that creates an application out of two terms.
module Terms : Pratter.SUPPORT with type term = term and type table = table =
struct
type nonrec term = term
type nonrec table = table
let get { prefix; infix; postfix } (t: term) =
match t with
 Symb id > (
try Some (Pratter.Prefix, List.assoc id prefix)
with Not_found > (
try
let bp, assoc = List.assoc id infix in
Some (Pratter.Infix assoc, bp)
with Not_found > (
try Some (Pratter.Postfix, List.assoc id postfix)
with Not_found > None) ) )
 _ > None
let make_appl t u = Appl (t, u)
end
module Parser = Pratter.Make (Terms)
Then that's it, we can parse streams of terms with operators. For instance, assume that we want to parse x ! + y * z
where
+
and*
are infix operators, with*
having a higher binding power than+
;
is a prefix operator having a higher binding power than+
and*
,!
is a postfix operator.
Create a table holding these operators:
let tbl =
{ prefix = [ "", 1.0 ]
; infix = [ ("+", (0.5, Pratter.Left)) ; ("*", (0.6, Pratter.Left)) ]
; postfix = [ "!", 1.0 ] }
Priority (also called binding power) can be any float, and associativity may be Pratter.Left
, Pratter.Right
or Pratter.Neither
.
Finally parse the input using Parser.expression
:
let input = [ Symb "x"; Symb "!"; Symb "+"; Symb "y"; Symb "*"; Symb ""; Symb "z"]
Parser.expression tbl (Stream.of_list input)
we obtain the term (x !) + (y * (z))
(wrapped into a result
) represented by
Appl (Appl (Symb "+", Appl (Symb "!", Symb "x")),
Appl (Appl (Symb "*", Symb "y"), Appl (Symb "", Symb "z")))
Dependencies (3)
 camlpstreams

dune
>= "2.7"

ocaml
>= "4.08"
Dev Dependencies (4)

odoc
withdoc

qcheckalcotest
withtest

qcheck
withtest & >= "0.12"

alcotest
withtest
Used by (1)

lambdapi
>= "2.2.1" & < "2.4.1"