parent
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33
README.adoc
33
README.adoc
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@ -25,8 +25,8 @@ The parser, however, does a bunch of transformations:
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* `[a b c]` makes a call to `(list a b c)`;
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* `@var` is a shorthand for `(set var)`;
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* `{ code }` is the most complex one. Each line within the curly braces is
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wrapped in parentheses, and the resulting list is quoted, so that it doesn't
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execute immediately.
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wrapped in parentheses, and the resulting sequence is wrapped in a quoted
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list, so that it doesn't execute immediately.
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As an example, consider the following snippet:
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@ -38,13 +38,13 @@ As an example, consider the following snippet:
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which gets expanded to the following:
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((print (if (quote ((eq? (set var) foo)))
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(quote ((values 'Hello world\n')))
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((print (if (block (eq? (set var) foo))
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(block (values 'Hello world\n'))
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else
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(quote ((values 'Error\n'))))))
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(block (values 'Error\n')))))
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Observe that the whole program is enclosed in an implicit pair of `{}` and that
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`quote` is a very powerful special form which can replace many others if needed.
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`block` is all that's left of special forms.
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For a slightly more realistic example you can have a look at 'greet.ell'.
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@ -55,20 +55,27 @@ of lists) are assigned to local variables named `1`, `2`, etc., and the full
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list of them is stored in `args`.
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When evaluating a command, the first argument is typically a string with its
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name and it is resolved as if `set` was called on it.
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name and it is resolved as if `set` was called on it. Lists are left for
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execution as they are.
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The last expression in a block is the return value.
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Special Forms
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-------------
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`quote [<arg>]...`
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`block [<arg>]...`
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Like `values` but returns the arguments without any evaluation.
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Like `list` but doesn't evaluate arguments. A more appropriate name might be
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`quoted-list`, which is not as descriptive in terms of syntax. If simple
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quoting is desired, the list can be unpacked by an ordinary command.
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Standard library
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Standard Library
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----------------
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The standard library interprets the empty list and the empty string as false
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values, everything else is taken as true.
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values, everything else is considered true. Numbers are floating point with
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double precision, trailing zeroes are truncated.
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Where a `<body>` is expected, strings retain their value, and block evaluation
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is postponed as necessary.
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`local <names> [<value>]...`
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@ -89,7 +96,7 @@ Return an arbitrary number of values.
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`if <cond> <body> [elif <cond> <body>]... [else <body>]`
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Conditional evaluation, strings evaluate to themselves.
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Conditional evaluation.
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`for <list> <body>`
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@ -129,7 +136,7 @@ Execute the body and pass any error to the handler instead of propagating it.
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`throw <message>`
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Throw an error. Messages starting on an underscore don't generate backtraces
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Throw an error. Messages starting on an underscore don't generate backtraces,
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which can be used to catch them.
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`not <value>`
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16
ell.c
16
ell.c
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@ -383,12 +383,10 @@ print_string (struct item *s) {
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static bool
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print_block (struct item *list) {
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if (!list->head || strcmp (list->head->value, "quote")
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|| !list->head->next || list->head->next->next
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|| list->head->next->type != ITEM_LIST)
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if (!list->head || strcmp (list->head->value, "block"))
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return false;
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list = list->head->next->head;
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list = list->head->next;
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for (struct item *line = list; line; line = line->next)
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if (line->type != ITEM_LIST)
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return false;
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@ -579,8 +577,7 @@ parse_item (struct parser *self, jmp_buf out) {
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while ((*tail = parse_line (self, err)))
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tail = &(*tail)->next;
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EXPECT (T_RBRACE);
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result = CHECK (new_list (result));
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return CHECK (parse_prefix_list (result, "quote"));
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return CHECK (parse_prefix_list (result, "block"));
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}
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self->memory_failure = !(self->error = lexer_errorf (&self->lexer,
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@ -843,8 +840,9 @@ execute_item (struct context *ctx, struct item *body, struct item **result) {
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struct item *args = body->next;
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if (body->type == ITEM_STRING) {
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const char *name = body->value;
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if (!strcmp (name, "quote"))
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return !args || check (ctx, (*result = new_clone_list (args)));
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if (!strcmp (name, "block"))
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return (!args || check (ctx, (args = new_clone_list (args))))
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&& check (ctx, (*result = new_list (args)));
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if ((body = get (ctx, name)))
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return execute_resolved (ctx, body, args, result);
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return execute_native (ctx, name, args, result);
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@ -857,7 +855,7 @@ execute_item (struct context *ctx, struct item *body, struct item **result) {
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return false;
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// It might a bit confusing that this doesn't evaluate arguments
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// but neither does "quote" and there's nothing to do here
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// but neither does "block" and there's nothing to do here
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if (!evaluated)
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return true;
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