post-scarcity/src/read.c

/**
 * read.c
 *
 * First pass at a reader, for bootstrapping.
 *
 *
 * (c) 2017 Simon Brooke <simon@journeyman.cc>
 * Licensed under GPL version 2.0, or, at your option, any later version.
 */

#include <math.h>
#include <stdbool.h>
#include <stdio.h>
/*
 * wide characters 
 */
#include <wchar.h>
#include <wctype.h>

#include "consspaceobject.h"
#include "integer.h"
#include "intern.h"
#include "read.h"
#include "real.h"

/*
 * for the time being things which may be read are: strings numbers - either
 * integer or real, but not yet including ratios or bignums lists Can't read
 * atoms because I don't yet know what an atom is or how it's stored. 
 */

struct cons_pointer read_number(FILE * input, wint_t initial);
struct cons_pointer read_list(FILE * input, wint_t initial);
struct cons_pointer read_string(FILE * input, wint_t initial);
struct cons_pointer read_symbol(FILE * input, wint_t initial);

/**
 * quote reader macro in C (!)
 */
struct cons_pointer c_quote(struct cons_pointer arg)
{
    return make_cons(c_string_to_lisp_symbol("quote"), make_cons(arg, NIL));
}

/**
 * Read the next object on this input stream and return a cons_pointer to it,
 * treating this initial character as the first character of the object
 * representation.
 */
struct cons_pointer read_continuation(FILE * input, wint_t initial)
{
    struct cons_pointer result = NIL;

    wint_t c;

    for (c = initial;
         c == '\0' || iswblank(c) || iswcntrl(c); c = fgetwc(input));

    switch (c) {
    case '\'':
        result = c_quote(read_continuation(input, fgetwc(input)));
        break;
    case '(':
        result = read_list(input, fgetwc(input));
        break;
    case '"':
        result = read_string(input, fgetwc(input));
        break;
    default:
        if (iswdigit(c)) {
            result = read_number(input, c);
        } else if (iswprint(c)) {
            result = read_symbol(input, c);
        } else {
            fprintf(stderr, "Unrecognised start of input character %c\n", c);
        }
    }

    return result;
}

/**
 * read a number from this input stream, given this initial character.
 */
struct cons_pointer read_number(FILE * input, wint_t initial)
{
    int accumulator = 0;
    int places_of_decimals = 0;
    bool seen_period = false;
    wint_t c;

    fprintf(stderr, "read_number starting '%c' (%d)\n", initial, initial);

    for (c = initial; iswdigit(c) || c == btowc('.'); c = fgetwc(input)) {
        if (c == btowc('.')) {
            seen_period = true;
        } else {
            accumulator = accumulator * 10 + ((int) c - (int) '0');

            if (seen_period) {
                places_of_decimals++;
            }
        }
    }

    /*
     * push back the character read which was not a digit 
     */
    ungetwc(c, input);

    if (seen_period) {
        return make_real(accumulator / pow(10, places_of_decimals));
    } else {
        return make_integer(accumulator);
    }
}

/**
 * Read a list from this input stream, which no longer contains the opening
 * left parenthesis.
 */
struct cons_pointer read_list(FILE * input, wint_t initial)
{
    struct cons_pointer result = NIL;

    if (initial != ')') {
        fwprintf(stderr, L"read_list starting '%C' (%d)\n", initial, initial);
        struct cons_pointer car = read_continuation(input, initial);
        result = make_cons(car, read_list(input, fgetwc(input)));
    } else {
        fprintf(stderr, "End of list detected\n");
    }

    return result;
}

/** 
 * Read a string. This means either a string delimited by double quotes 
 * (is_quoted == true), in which case it may contain whitespace but may
 * not contain a double quote character (unless escaped), or one not
 * so delimited in which case it may not contain whitespace (unless escaped)
 * but may contain a double quote character (probably not a good idea!)
 */
struct cons_pointer read_string(FILE * input, wint_t initial)
{
    struct cons_pointer cdr = NIL;
    struct cons_pointer result;

    fwprintf(stderr, L"read_string starting '%C' (%d)\n", initial, initial);

    switch (initial) {
    case '\0':
        result = make_string(initial, NIL);
        break;
    case '"':
        result = make_string('\0', NIL);
        break;
    default:
        result = make_string(initial, read_string(input, fgetwc(input)));
        break;
    }

    return result;
}

struct cons_pointer read_symbol(FILE * input, wint_t initial)
{
    struct cons_pointer cdr = NIL;
    struct cons_pointer result;

    fwprintf(stderr, L"read_symbol starting '%C' (%d)\n", initial, initial);

    switch (initial) {
    case '\0':
        result = make_symbol(initial, NIL);
        break;
    case '"':
        /*
         * THIS IS NOT A GOOD IDEA, but is legal 
         */
        result = make_symbol(initial, read_symbol(input, fgetwc(input)));
        break;
    case ')':
        /*
         * unquoted strings may not include right-parenthesis 
         */
        result = make_symbol('\0', NIL);
        /*
         * push back the character read 
         */
        ungetwc(initial, input);
        break;
    default:
        if (iswblank(initial) || !iswprint(initial)) {
            result = make_symbol('\0', NIL);
            /*
             * push back the character read 
             */
            ungetwc(initial, input);
        } else {
            result = make_symbol(initial, read_symbol(input, fgetwc(input)));
        }
        break;
    }

    return result;
}

/**
 * Read the next object on this input stream and return a cons_pointer to it.
 */
struct cons_pointer read(FILE * input)
{
    return read_continuation(input, fgetwc(input));
}