From eeff5e273f22aa28e81ab080e9ffdce85ac394b8 Mon Sep 17 00:00:00 2001
From: Bad Diode <bd@badd10de.dev>
Date: Fri, 22 Oct 2021 09:59:31 +0200
Subject: Prepare skeleton for bytecode interpreter

---
 src/treewalk/parser.c | 139 ++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 139 insertions(+)
 create mode 100644 src/treewalk/parser.c

(limited to 'src/treewalk/parser.c')

diff --git a/src/treewalk/parser.c b/src/treewalk/parser.c
new file mode 100644
index 0000000..a2f0f71
--- /dev/null
+++ b/src/treewalk/parser.c
@@ -0,0 +1,139 @@
+#include "parser.h"
+
+Token
+peek_token(const Visitor *visitor) {
+    return visitor->tokens[visitor->current];
+}
+
+Token
+next_token(Visitor *visitor) {
+    return visitor->tokens[visitor->current++];
+}
+
+bool
+has_next_token(const Visitor *visitor) {
+    return visitor->current < array_size(visitor->tokens);
+}
+
+Object *
+parse_fixnum(Token tok) {
+    ssize_t num = 0;
+    int sign = 1;
+    for (size_t i = 0; i < tok.value.n; i++) {
+        char c = tok.value.start[i];
+        if (c == '-') {
+            sign = -1;
+            continue;
+        }
+        num = num * 10 + (c - '0');
+    }
+
+    Object *obj = make_fixnum(num * sign);
+    push_root(obj);
+    return obj;
+}
+
+Object *
+parse_list(Visitor *vs) {
+    Token tok = peek_token(vs);
+    if (tok.type == TOKEN_EOF) {
+        return obj_err;
+    }
+    Object *root = make_pair(obj_nil, obj_nil);
+    push_root(root);
+    Object *next_obj = parse_tree(vs);
+    if (next_obj == obj_err) {
+        return obj_err;
+    }
+    root->car = next_obj;
+    Object *list = root;
+    while (has_next_token(vs)) {
+        Token tok = peek_token(vs);
+        if (tok.type == TOKEN_RPAREN) {
+            next_token(vs);
+            break;
+        }
+        if (tok.type == TOKEN_EOF) {
+            return obj_err;
+        }
+        next_obj = parse_tree(vs);
+        if (next_obj == obj_err) {
+            return obj_err;
+        }
+        list->cdr = make_pair(next_obj, obj_nil);
+        list = list->cdr;
+    }
+    return root;
+}
+
+Object *
+parse_tree(Visitor *vs) {
+    Token tok = next_token(vs);
+    switch (tok.type) {
+        case TOKEN_FIXNUM: {
+            return parse_fixnum(tok);
+        } break;
+        case TOKEN_TRUE: {
+            return obj_true;
+        } break;
+        case TOKEN_FALSE: {
+            return obj_false;
+        } break;
+        case TOKEN_RPAREN: {
+            error_push((Error){
+                .type = ERR_TYPE_PARSER,
+                .value = ERR_UNBALANCED_PAREN,
+                .line = tok.line,
+                .col = tok.column,
+            });
+            return obj_err;
+        } break;
+        case TOKEN_QUOTE: {
+            Object *base = make_pair(obj_quote, obj_nil);
+            base->cdr = make_pair(obj_nil, obj_nil);
+            push_root(base);
+            Object *next_obj = parse_tree(vs);
+            if (next_obj == obj_err) {
+                return obj_err;
+            }
+            base->cdr->car = next_obj;
+            return base;
+        } break;
+        case TOKEN_LPAREN: {
+            Object *obj = parse_list(vs);
+            if (obj == obj_err) {
+                error_push((Error){
+                    .type = ERR_TYPE_PARSER,
+                    .value = ERR_UNBALANCED_PAREN,
+                    .line = tok.line,
+                    .col = tok.column,
+                });
+            }
+            return obj;
+        } break;
+        case TOKEN_STRING: {
+            Object *obj = make_string();
+            push_root(obj);
+            append_string(obj, tok.value);
+            return obj;
+        } break;
+        case TOKEN_SYMBOL: {
+            Object *obj = make_symbol(tok.value);
+            push_root(obj);
+            return obj;
+        } break;
+        case TOKEN_NIL: {
+            return obj_nil;
+        } break;
+        default: {
+            break;
+        } break;
+    }
+    error_push((Error){
+        .type = ERR_TYPE_PARSER,
+        .value = ERR_EOF_REACHED,
+        .line = tok.line,
+        .col = tok.column,
+    });
+    return obj_err;
+}
-- 
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