OCaml interpreter: evaluate a function inside a function

Question

I'm trying to write an interpreter in OCaml and I have a problem here.

In my program, I want to call a function like this, for example:

print (get_line 4)  // print: print to stdout, get_line: get a specific line in a file

How can I do that? The problem is in our parser, I think so as it defines how a program will be run, how a function is defined and the flow of a program. This is what I have so far in parser an lexer (code below), but it didn't seem to work. I don't really see any difference between my code and the calculator on OCaml site, the statement inside the bracket is evaluated firstly, then return its value to its parent operation to do the next evaluating.

In my interpreter, the function get_line inside bracket is evaluate firstly, but I don't think it returns the value to print function, or it does but wrong type (checked, but I don't think it's this error).

One difference between calculator and my interpreter is that the calculator is working with primitive types, mine are functions. But they should be similar.

This is my code, just a part of it:

parser.mly:

%token ODD
%token CUT
%start main
%type <Path.term list> main
%%

main:
    | expr EOL main {$1 :: $3}
    | expr EOF { [$1] }
    | EOL main { $2 }
;
expr:
        | ODD INT  { Odd $2}
    | ODD LPAREN INT RPAREN  expr { Odd $3 }
        | CUT INT INT { Cut ($2, $3)}
    | CUT INT INT expr { Cut ($2, $3) }

lexer.mll:

{
    open Parser
}
(* define all keyword used in the program *)
rule main =
    parse
        | ['\n'] { EOL }
        | ['\r']['\n'] { EOL }
        | [' ''\t''\n']     { main lexbuf }     
        | '('       { LPAREN }
        | ')'       { RPAREN }
        | "cut" { CUT }     
        | "trunclength" { TRUNCLENGTH }
        | "firstArithmetic" { FIRSTARITH }
        | "f_ArithmeticLength" { F_ARITHLENGTH }
        | "secondArithmetic" { SECARITH }
        | "s_ArithmeticLength" { S_ARITHLENGTH }
        | "odd" { ODD }
        | "oddLength" { ODDLENGTH }
        | "zip" { ZIP }
        | "zipLength" { ZIPLENGTH }
        | "newline" { NEWLINE }
        | eof  { EOF }              
        | ['0' - '9']+ as lxm { INT(int_of_string lxm) }
        | ['a'-'z''A'-'Z'] ['a'-'z''A'-'Z''0'-'9']* as lxm { STRING lxm  }

nlucaroni nlucaroni · Accepted Answer · 2014-03-19T13:20:10

| ODD LPAREN INT RPAREN  expr { Odd $3 }

Your grammar rule requires an INT between parenthesis. You need to change that to an expr. There are a number of other issues with this, but I'll leave it at that.

OCaml interpreter: evaluate a function inside a function

2 Answers