From 4ebcd99d1fadac72ea58ea46012a86c5319ef7e7 Mon Sep 17 00:00:00 2001
From: Bad Diode <bd@badd10de.dev>
Date: Sat, 30 Oct 2021 08:16:08 +0200
Subject: Add parsing of lambda expression

---
 src/parser.c | 130 ++++++++++++++++++++++++++++++++++++++++++++++++-----------
 1 file changed, 106 insertions(+), 24 deletions(-)

(limited to 'src/parser.c')

diff --git a/src/parser.c b/src/parser.c
index 2d70c9d..8a6c4ce 100644
--- a/src/parser.c
+++ b/src/parser.c
@@ -1,6 +1,9 @@
 #include "parser.h"
 #include "darray.h"
 
+static Object **objects = NULL;
+static Root *roots = NULL;
+
 Token
 peek_token(const Parser *parser) {
     return parser->tokens[parser->current];
@@ -67,20 +70,82 @@ parse_symbol(Token tok) {
     return ret;
 }
 
+Object *
+parse_lambda(Parser *parser, Errors *errors) {
+    Token start = next_token(parser);
+    Object *lambda = object_alloc(start, OBJ_TYPE_LAMBDA);
+    array_init(lambda->params, 0);
+    array_init(lambda->body, 0);
+
+    // Parse parameters.
+    Token tok = next_token(parser);
+    if (tok.type == TOKEN_LPAREN) {
+        while (has_next_token(parser)) {
+            Token tok = next_token(parser);
+            if (tok.type == TOKEN_RPAREN) {
+                break;
+            }
+            if (tok.type != TOKEN_SYMBOL) {
+                error_push(errors, (Error){
+                    .type = ERR_TYPE_PARSER,
+                    .value = ERR_WRONG_ARG_TYPE,
+                    .line = tok.line,
+                    .col = tok.col,
+                });
+            }
+            Object *symbol = parse_symbol(tok);
+            array_push(lambda->params, symbol);
+        }
+    } else if (tok.type != TOKEN_NIL) {
+        error_push(errors, (Error){
+            .type = ERR_TYPE_PARSER,
+            .value = ERR_WRONG_ARG_TYPE,
+            .line = tok.line,
+            .col = tok.col,
+        });
+    }
+
+    // Parse body.
+    while (has_next_token(parser)) {
+        Token tok = peek_token(parser);
+        if (tok.type == TOKEN_RPAREN) {
+            next_token(parser);
+            break;
+        }
+        Object *expr = parse_tree(parser, errors);
+        array_push(lambda->body, expr);
+    }
+    return lambda;
+}
+
 Object *
 parse_list(Parser *parser, Errors *errors) {
     if (errors->n != 0) {
         return NULL;
     }
+
+    Token tok = peek_token(parser);
+    if (tok.type == TOKEN_RPAREN) {
+        error_push(errors, (Error){
+            .type = ERR_TYPE_PARSER,
+            .value = ERR_UNBALANCED_PAREN,
+            .line = tok.line,
+            .col = tok.col,
+        });
+        return NULL;
+    }
+    if (tok.type == TOKEN_LAMBDA) {
+        return parse_lambda(parser, errors);
+    }
+
     Token start = previous_token(parser);
     Object *root = object_alloc(start, OBJ_TYPE_PAIR);
-    root->car = NULL;
-    root->cdr = NULL;
+    root->head = NULL;
+    root->tail = NULL;
     Object *current = root;
     while (has_next_token(parser)) {
-        current->car = parse_tree(parser, errors);
-        if (errors->n != 0 || current->car == NULL) {
-            object_free(root);
+        current->head = parse_tree(parser, errors);
+        if (errors->n != 0 || current->head == NULL) {
             return NULL;
         }
 
@@ -91,12 +156,11 @@ parse_list(Parser *parser, Errors *errors) {
         }
 
         Object *next = object_alloc(start, OBJ_TYPE_PAIR);
-        next->car = NULL;
-        next->cdr = NULL;
-        current->cdr = next;
-        current = current->cdr;
+        next->head = NULL;
+        next->tail = NULL;
+        current->tail = next;
+        current = current->tail;
     }
-    object_free(root);
     error_push(errors, (Error){
         .type = ERR_TYPE_PARSER,
         .value = ERR_UNBALANCED_PAREN,
@@ -156,7 +220,7 @@ parse_tree(Parser *parser, Errors *errors) {
 
 Root *
 parse(Token *tokens, Errors *errors) {
-    Root *roots = NULL;
+    // Build initial AST.
     array_init(roots, 0);
     Parser parser = {
         .tokens = tokens,
@@ -170,15 +234,24 @@ parse(Token *tokens, Errors *errors) {
         }
         array_push(roots, root);
     }
+
+    // Perform semantic analysis.
+    // 1. Ensure core grammar is correct.
+    // 2. Check that symbols are defined before usage.
+    // 3. Remove unnecessary statements.
     return roots;
 }
 
 Object *
 object_alloc(Token tok, ObjectType type) {
+    if (objects == NULL) {
+        array_init(objects, 0);
+    }
     Object *node = malloc(sizeof(Object));
     node->line = tok.line;
     node->col = tok.col;
     node->type = type;
+    array_push(objects, node);
     return node;
 }
 
@@ -190,35 +263,36 @@ object_free(Object *node) {
     if (IS_STRING(node) || IS_SYMBOL(node)) {
         array_free(node->text);
     }
-    if (IS_PAIR(node)) {
-        object_free(node->car);
-        object_free(node->cdr);
+    if (IS_LAMBDA(node)) {
+        array_free(node->params);
+        array_free(node->body);
     }
     free(node);
 }
 
 void
-free_roots(Root *roots) {
-    if (roots != NULL) {
-        for (size_t i = 0; i < array_size(roots); i++) {
-            object_free(roots[i]);
+free_objects(void) {
+    if (objects != NULL) {
+        for (size_t i = 0; i < array_size(objects); i++) {
+            object_free(objects[i]);
         }
-        array_free(roots);
+        array_free(objects);
     }
+    array_free(roots);
 }
 
 void
 display_pair(Object *obj) {
-    object_display(obj->car);
-    if (obj->cdr == NULL) {
+    object_display(obj->head);
+    if (obj->tail == NULL) {
         return;
     }
-    if (IS_PAIR(obj->cdr)) {
+    if (IS_PAIR(obj->tail)) {
         printf(" ");
-        display_pair(obj->cdr);
+        display_pair(obj->tail);
     } else {
         printf(" . ");
-        object_display(obj->cdr);
+        object_display(obj->tail);
     }
 }
 
@@ -252,6 +326,14 @@ object_display(Object *obj) {
             display_pair(obj);
             printf(")");
         } break;
+        case OBJ_TYPE_LAMBDA: {
+            printf("#{lambda( ");
+            for (size_t i = 0; i < array_size(obj->params); i++) {
+                object_display(obj->params[i]);
+                printf(" ");
+            }
+            printf(")}");
+        } break;
     }
     return;
 }
-- 
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