Markdown to Plain Text

To render a Markdown tree as plain text.

§1. Main rendering recursion. Do not call this function directly: use the API in Markdown Rendering.

void MDRenderPlain::recurse(OUTPUT_STREAM, markdown_render *rdr, markdown_item *md, int mode) {
    if (rdr == NULL) internal_error("no render details in recursion");
    if (md == NULL) return;
    if (MarkdownVariations::intervene_in_rendering(rdr->variation, rdr, OUT, md, mode)) return;
    int old_mode = mode;
    switch (md->type) {
        /* Container blocks */
        case BLOCK_QUOTE_MIT:           Render a block quote1.2; break;
        case ALERT_MIT:                 Render an alert1.3; break;
        case UNORDERED_LIST_MIT:        Render a list1.4; break;
        case ORDERED_LIST_MIT:          Render a list1.4; break;
        case UNORDERED_LIST_ITEM_MIT:   Render a list item1.5; break;
        case ORDERED_LIST_ITEM_MIT:     Render a list item1.5; break;
        case FOOTNOTE_BODY_MIT:         Render a footnote body1.6; break;

        /* Leaf blocks */
        case PARAGRAPH_MIT:             Render a paragraph1.7; break;
        case THEMATIC_MIT:              Render a thematic break1.8; break;
        case HEADING_MIT:               Render a heading1.9; break;
        case CODE_BLOCK_MIT:            Render a code block1.10; break;
        case HTML_MIT:                  Render a raw HTML block1.11; break;
        case EMPTY_MIT:                 break;
        case TABLE_MIT:           Render a table1.12; break;
        case TICKBOX_MIT:               Render a tickbox1.13; break;

        /* Inline types */
        case PLAIN_MIT:                 Render plain text1.14; break;
        case LINE_BREAK_MIT:            Render a line break1.15; break;
        case SOFT_BREAK_MIT:            Render a soft line break1.16; break;
        case EMPHASIS_MIT:              Render emphasised text1.17; break;
        case STRONG_MIT:                Render strongly emphasised text1.18; break;
        case CODE_MIT:                  Render inline code sample1.19; break;
        case URI_AUTOLINK_MIT:          Render URI link1.20; break;
        case EMAIL_AUTOLINK_MIT:        Render email link1.21; break;
        case INLINE_HTML_MIT:           Render inline HTML content1.22; break;
        case LINK_MIT:                  Render link1.23; break;
        case IMAGE_MIT:                 Render image1.24; break;
        case LINK_DEST_MIT:             Render link destination1.25; break;
        case STRIKETHROUGH_MIT:         Render struck-through text1.26; break;
        case XMPP_AUTOLINK_MIT:         Render email link1.21; break;
        case TEX_MIT:                   Render maths matter in TeX1.27; break;
        case DISPLAYED_TEX_MIT:         Render maths matter in TeX1.27; break;
        case INWEB_LINK_MIT:            Render Inweb link1.28; break;

        default:                        Recurse1.1; break;
    }
    mode = old_mode;
}

§1.1. Again, note that EXISTING_PAR_MDRMODE propagates only down the leading edge of the tree: see Markdown to HTML for the reason.

Recurse1.1 =

    int m = mode;
    for (markdown_item *c = md->down; c; c = c->next) {
        MDRenderPlain::recurse(OUT, rdr, c, m);
        m = m & (~EXISTING_PAR_MDRMODE);
    }

This code is used in §1, §1.2, §1.3, §1.4, §1.6, §1.7, §1.9, §1.17 and §1.18 and §1.26.

§1.2. Container block items. Render a block quote1.2 =

    INDENT;
    WRITE("\n");
    Recurse1.1;
    WRITE("\n");
    OUTDENT;

This code is used in §1.

§1.3. Render an alert1.3 =

    int type = Markdown::get_alert_type(md);
    text_stream *name = MarkdownVariations::get_alert_form_name(rdr->variation, type);
    inchar32_t icon = MarkdownVariations::get_alert_form_icon(rdr->variation, type);
    WRITE("\n");
    if (icon) WRITE("! ");
    if (Str::len(name) > 0) {
        PUT(Str::get_at(name, 0));
        for (int i=1; i<Str::len(name); i++) PUT(Characters::tolower(Str::get_at(name, i)));
    } else {
        WRITE("Alert");
    }
    WRITE("\n");
    Recurse1.1;
    WRITE("\n");

This code is used in §1.

§1.4. Render a list1.4 =

    INDENT; WRITE("\n");
    mode = mode & (~LOOSE_MDRMODE);
    for (markdown_item *ch = md->down; ch; ch = ch->next) {
        if ((ch->next) && (ch->whitespace_follows))
            mode = mode | LOOSE_MDRMODE;
        for (markdown_item *gch = ch->down; gch; gch = gch->next)
            if ((gch->next) && (gch->whitespace_follows))
                mode = mode | LOOSE_MDRMODE;
    }
    Recurse1.1;
    WRITE("\n"); OUTDENT;

This code is used in §1 (twice).

§1.5. Render a list item1.5 =

    if (Markdown::get_item_number(md) > 0)
        WRITE("\n* ", Markdown::get_item_number(md));
    else
        WRITE("\n* ");
    int nl_issued = FALSE;
    for (markdown_item *ch = md->down; ch; ch = ch->next)
        if (((mode & LOOSE_MDRMODE) == 0) && (ch->type == PARAGRAPH_MIT)) {
            for (markdown_item *gch = ch->down; gch; gch = gch->next)
                MDRenderPlain::recurse(OUT, rdr, gch, mode);
        } else {
            if (nl_issued == FALSE) { nl_issued = TRUE; WRITE("\n"); }
            MDRenderPlain::recurse(OUT, rdr, ch, mode);
        }
    WRITE("\n");

This code is used in §1 (twice).

§1.6. Render a footnote body1.6 =

    WRITE("[%d] ", md->details);
    Recurse1.1;

This code is used in §1.

§1.7. Leaf blocks. Render a paragraph1.7 =

    mode = mode & (~EXISTING_PAR_MDRMODE);
    Recurse1.1;
    WRITE("\n\n");

This code is used in §1.

§1.8. Render a thematic break1.8 =

    WRITE("\n\n-----------------------------------------------------------------\n\n");

This code is used in §1.

§1.9. Render a heading1.9 =

    WRITE("\n{\\bf ");
    Recurse1.1;
    WRITE("}\n");
    WRITE("\n");

This code is used in §1.

§1.10. We use the convention that the first word of the info string on a fenced code block is the "language", and give it a CSS class accordingly. A piquant part of CommonMark is that the language does respect entities, but that the body of the code block does not. (It also respects backslash escapes, but we do not render the language in ESCAPES_MDRMODE mode because those have already been taken out at the parsing stage.)

Render a code block1.10 =

    mode = mode & (~ESCAPES_MDRMODE) & (~ENTITIES_MDRMODE);
    TEMPORARY_TEXT(language)
    for (int i=0; i<Str::len(md->info_string); i++) {
        inchar32_t c = Str::get_at(md->info_string, i);
        if ((c == ' ') || (c == '\t')) break;
        PUT_TO(language, c);
    }
    TEMPORARY_TEXT(language_rendered)
    if (Str::len(language) > 0) {
        md->sliced_from = language;
        md->from = 0; md->to = Str::len(language) - 1;
        if (MarkdownVariations::supports(rdr->variation, ENTITIES_MARKDOWNFEATURE))
            MDRender::slice(language_rendered, rdr, md, mode | ENTITIES_MDRMODE);
        else
            MDRender::slice(language_rendered, rdr, md, mode);
    }
    DISCARD_TEXT(language)

    MDRenderPlain::render_code_block(OUT, mode, rdr, md->stashed, language_rendered);
    DISCARD_TEXT(language_rendered)

This code is used in §1.

§1.11. Nothing can usefully be done here.

Render a raw HTML block1.11 =

    for (int i=0; i<Str::len(md->stashed); i++)
        MDRenderPlain::char(OUT, Str::get_at(md->stashed, i), 0);

This code is used in §1.

§1.12. Render a table1.12 =

    markdown_item *alignment_markers = md->down;
    if (alignment_markers) {
        int row_count = 0;
        for (markdown_item *md = alignment_markers->next; md; md = md->next) row_count++;
        if (row_count > 0) {
            WRITE("\n");
            textual_table *T = TextualTables::new_table();
            markdown_item *row = alignment_markers->next;
            int r = 0;
            while (row) {
                if (r++ > 0) TextualTables::begin_row(T);
                for (markdown_item *md = row->down, *top = alignment_markers->down;
                    md; md = md->next, top = top->next) {
                    if (md->down) {
                        TEMPORARY_TEXT(cell)
                        MDRenderPlain::recurse(cell, rdr, md->down, mode);
                        WRITE_TO(TextualTables::next_cell(T), "%S", cell);
                        DISCARD_TEXT(cell)
                    }
                }
                row = row->next;
            }
            TextualTables::tabulate(OUT, T);
            WRITE("\n");
        }
    }

This code is used in §1.

§1.13. Render a tickbox1.13 =

    if (Markdown::get_tick_state(md)) {
        WRITE("[x] ");
    } else {
        WRITE("[ ] ");
    }

This code is used in §1.

§1.14. Inline types. The fuss over ALT_TEXT_MDRMODE does not arise for plain text, since alt-text does not exist in the absence of images, and even if it did, it would just be plain text in the same way that all other material is. So we don't check for this.

Render plain text1.14 =

    MDRender::slice(OUT, rdr, md, mode);

This code is used in §1.

§1.15. Render a line break1.15 =

    MDRenderPlain::char(OUT, '\n', mode);

This code is used in §1.

§1.16. Render a soft line break1.16 =

    MDRenderPlain::char(OUT, '\n', mode);

This code is used in §1.

§1.17. Render emphasised text1.17 =

    Recurse1.1;

This code is used in §1.

§1.18. Render strongly emphasised text1.18 =

    Recurse1.1;

This code is used in §1.

§1.19. Render inline code sample1.19 =

    mode = mode & (~ESCAPES_MDRMODE);
    mode = mode & (~ENTITIES_MDRMODE);
    mode = mode | (INLINECODE_MDRMODE);
    MDRender::slice(OUT, rdr, md, mode);

This code is used in §1.

§1.20. Render URI link1.20 =

    text_stream *supplied_scheme = NULL;
    if (Markdown::get_add_protocol_state(md)) supplied_scheme = I"http://";
    Render autolink1.20.1;

This code is used in §1.

§1.21. Render email link1.21 =

    text_stream *supplied_scheme = NULL;
    if (Markdown::get_add_protocol_state(md)) {
        supplied_scheme = I"mailto:";
        if (md->type == XMPP_AUTOLINK_MIT) supplied_scheme = I"xmpp:";
    }
    Render autolink1.20.1;

This code is used in §1 (twice).

§1.20.1. Render autolink1.20.1 =

    TEMPORARY_TEXT(address)
    MDRender::slice(address, rdr, md, (mode & (~ESCAPES_MDRMODE)) | URI_MDRMODE);
    MDRender::stream(OUT, rdr, address, mode);
    DISCARD_TEXT(address)

This code is used in §1.20 and §1.21.

§1.22. Render inline HTML content1.22 =

    mode = mode | RAW_MDRMODE;
    if (Markdown::get_filtered_state(md)) mode = mode | FILTERED_MDRMODE;
    mode = mode & (~ESCAPES_MDRMODE);
    mode = mode & (~ENTITIES_MDRMODE);
    MDRender::slice(OUT, rdr, md, mode);

This code is used in §1.

§1.23. Render link1.23 =

    TEMPORARY_TEXT(URI)
    TEMPORARY_TEXT(title)
    if (md->details > 0) {
        Render footnote instead1.23.1;
    } else if (md->down->next) {
        if (md->down->next->type == LINK_DEST_MIT) {
            MDRenderPlain::recurse(URI, rdr, md->down->next, mode | URI_MDRMODE);
            if ((md->down->next->next) && (md->down->next->next->type == LINK_TITLE_MIT))
                MDRenderPlain::recurse(title, rdr, md->down->next->next, mode);
        } else if (md->down->next->type == LINK_TITLE_MIT) {
            MDRenderPlain::recurse(title, rdr, md->down->next, mode);
        }
        MDRenderPlain::recurse(OUT, rdr, md->down, mode);
    }
    DISCARD_TEXT(URI)
    DISCARD_TEXT(title)

This code is used in §1.

§1.23.1. Render footnote instead1.23.1 =

    markdown_item *body = MDRender::seek_footnote_body(rdr, md->details);
    if (body == NULL) WRITE("[Missing footnote?]");
    else WRITE("[%d]", md->details);

This code is used in §1.23.

§1.24. Render image1.24 =

    TEMPORARY_TEXT(URI)
    TEMPORARY_TEXT(title)
    TEMPORARY_TEXT(alt)
    if (md->down->next) {
        if (md->down->next->type == LINK_DEST_MIT) {
            MDRenderPlain::recurse(URI, rdr, md->down->next, mode);
            if ((md->down->next->next) && (md->down->next->next->type == LINK_TITLE_MIT))
                MDRenderPlain::recurse(title, rdr, md->down->next->next, mode);
        } else if (md->down->next->type == LINK_TITLE_MIT) {
            MDRenderPlain::recurse(title, rdr, md->down->next, mode);
        }
    }
    MDRenderPlain::recurse(alt, rdr, md->down, mode | ALT_TEXT_MDRMODE);
    int skip_image_rendering = FALSE;
    if (MarkdownVariations::supports(rdr->variation, GADGETS_MARKDOWNFEATURE))
        skip_image_rendering =
            MDRender::render_gadget(OUT, rdr, mode, alt, URI);

    if (skip_image_rendering == FALSE) {
        int w = -1, h = -1;
        if (rdr) {
            int j = 0;
            for (int i=1; i<Str::len(URI)-1; i++)
                if (Str::get_at(URI, i) == '@')
                    j = i;
            if (j > 0) {
                int x = 0;
                for (int i=j+1; i<Str::len(URI); i++)
                    if (Str::get_at(URI, i) == 'x')
                        x = i;
                int bad = FALSE;
                for (int i=j+1; i<Str::len(URI); i++)
                    if ((i != x) && (Characters::isdigit(Str::get_at(URI, i)) == FALSE))
                        bad = TRUE;
                if (bad == FALSE) {
                    if (x > 0) {
                        if (x > j+1) w = Str::atoi(URI, j+1);
                        if (x < Str::len(URI) - 1) h = Str::atoi(URI, x+1);
                    } else {
                        w = Str::atoi(URI, j+1);
                    }
                    Str::truncate(URI, j);
                }
            }
        }
        if (Str::len(alt) > 0) WRITE("[Image: %S]\n", alt);
        else WRITE("[IMAGE %S HERE]\n", URI);
    }
    DISCARD_TEXT(URI)
    DISCARD_TEXT(title)
    DISCARD_TEXT(alt)

This code is used in §1.

§1.25. Render link destination1.25 =

    mode = mode | URI_MDRMODE;
    MDRender::slice(OUT, rdr, md->down, mode);

This code is used in §1.

§1.26. Render struck-through text1.26 =

    Recurse1.1;

This code is used in §1.

§1.27. Render maths matter in TeX1.27 =

    TEMPORARY_TEXT(TEX)
    if (MarkdownVariations::supports(rdr->variation, ALT_TEX_MARKDOWNFEATURE)) {
        int m = RAW_MDRMODE;
        for (markdown_item *c = md->down; c; c = c->next) {
            MDRenderPlain::recurse(TEX, rdr, c, m);
            m = m & (~EXISTING_PAR_MDRMODE);
        }
    } else {
        for (int i=md->from; i<=md->to; i++) {
            inchar32_t c = Markdown::get_at(md, i);
            PUT_TO(TEX, c);
        }
    }
    TEMPORARY_TEXT(PARAPHRASE)
    MDRender::remove_math_mode(OUT, TEX, TRUE);
    if (md->type == DISPLAYED_TEX_MIT) {
        WRITE("\n\n");
        int width = Str::len(PARAPHRASE);
        if (width < 80) for (int i=0; i<(80-width)/2; i++) PUT(' ');
        WRITE("%S", PARAPHRASE);
        WRITE("\n\n");
    } else {
        WRITE("%S", PARAPHRASE);
    }
    DISCARD_TEXT(PARAPHRASE)

This code is used in §1 (twice).

§1.28. Render Inweb link1.28 =

    MDRenderPlain::recurse(OUT, rdr, md->down, mode);

This code is used in §1.

§2. Character output.

void MDRenderPlain::char(OUTPUT_STREAM, inchar32_t c, int mode) {
    if (mode & TOLOWER_MDRMODE) c = Characters::tolower(c);
    if (mode & URI_MDRMODE) {
        if (c >= 0x10000) {
            MARKDOWNPLAIN_URI_HEX(0xF0 + (unsigned char) (c >> 18));
            MARKDOWNPLAIN_URI_HEX(0x80 + (unsigned char) ((c >> 12) & 0x3f));
            MARKDOWNPLAIN_URI_HEX( 0x80 + (unsigned char) ((c >> 6) & 0x3f));
            MARKDOWNPLAIN_URI_HEX(0x80 + (unsigned char) (c & 0x3f));
        } else if (c >= 0x800) {
            MARKDOWNPLAIN_URI_HEX(0xE0 + (unsigned char) (c >> 12));
            MARKDOWNPLAIN_URI_HEX(0x80 + (unsigned char) ((c >> 6) & 0x3f));
            MARKDOWNPLAIN_URI_HEX(0x80 + (unsigned char) (c & 0x3f));
        } else if (c >= 0x80) {
            MARKDOWNPLAIN_URI_HEX(0xC0 + (unsigned char) (c >> 6));
            MARKDOWNPLAIN_URI_HEX(0x80 + (unsigned char) (c & 0x3f));
        } else {
            switch (c) {
                case '[': MARKDOWNPLAIN_URI_HEX((unsigned char) c); break;
                case '\\':MARKDOWNPLAIN_URI_HEX((unsigned char) c); break;
                case '\"':MARKDOWNPLAIN_URI_HEX((unsigned char) c); break;
                case ']': MARKDOWNPLAIN_URI_HEX((unsigned char) c); break;
                case '`': MARKDOWNPLAIN_URI_HEX((unsigned char) c); break;
                case ' ': MARKDOWNPLAIN_URI_HEX((unsigned char) c); break;
                default: PUT(c); break;
            }
        }
    } else {
        PUT(c);
    }
}

§3. Where:

define MARKDOWNPLAIN_URI_HEX(x) {
        unsigned int z = (unsigned int) x;
        PUT('%');
        MDRender::hex_digit(OUT, z >> 4);
        MDRender::hex_digit(OUT, z & 0x0f);
    }

§4. Code block rendering. This is very simple, since syntax-colouring can be ignored completely.

void MDRenderPlain::render_code_block(OUTPUT_STREAM, int mode, markdown_render *rdr,
    text_stream *code, text_stream *language_name) {
    MDRender::stream(OUT, rdr, code, INLINECODE_MDRMODE);
}

Markdown to LaTeX❮
PreliminariesP
Chapter 1: Setting Up1
Chapter 2: Memory, Streams and Collections2
Chapter 3: The Operating System3
Chapter 4: Text Handling4
Chapter 5: Generating Websites5
HTMLhtm
HTML Entitieshe
Markdownmrk
Markdown Phase Impi
Markdown Phase IImpi2
Markdown Renderingmr
Markdown to HTMLmth
Markdown to TeXmtt
Markdown to LaTeXmtl
Markdown to Plain Textmtpt
Markdown Variationsmv
Inform-Flavoured Markdownim
Epub Ebooksee
Chapter 6: Media6
Chapter 7: Semantic Versioning7
Markdown Variations❯