Build Your Own Lisp: Learn C and Build Your Own Programming Language by Daniel Holden

Author:Daniel Holden [Holden, Daniel]
Language: eng
Format: epub
Tags: C, LISP, Компиляция и интерпретация
ISBN: 9781501006623
Google: GSALogEACAAJ
Amazon: 1501006622
Goodreads: 24666409
Publisher: CreateSpace Independent Publishing Platform
Published: 2014-10-21T20:00:00+00:00

Builtin Functions

* * *

We can read in Q-Expressions but they are still useless. We need some way to manipulate them.

For this we can define some built-in operators to work on our list type. Choosing a concise set of these is important. If we implement a few fundamental operations then we can use these to define new operations without adding extra C code. There are a few ways to pick these fundamental operators but I've chosen a set that will allow us to do everything we need. They are defined as follows.

list Takes one or more arguments and returns a new Q-Expression containing the arguments

head Takes a Q-Expression and returns a Q-Expression with only of the first element

tail Takes a Q-Expression and returns a Q-Expression with the first element removed

join Takes one or more Q-Expressions and returns a Q-Expression of them conjoined together

eval Takes a Q-Expression and evaluates it as if it were a S-Expression

Like with our mathematical operators we should add these functions as possible valid symbols. Afterward we can go about trying to define their behaviour in a similar way to builtin_op.

mpca_lang(MPCA_LANG_DEFAULT, " \ number : /-?[0-9]+/ ; \ symbol : \"list\" | \"head\" | \"tail\" \ | \"join\" | \"eval\" | '+' | '-' | '*' | '/' ; \ sexpr : '(' <expr>* ')' ; \ qexpr : '{' <expr>* '}' ; \ expr : <number> | <symbol> | <sexpr> | <qexpr> ; \ lispy : /^/ <expr>* /$/ ; \ ", Number, Symbol, Sexpr, Qexpr, Expr, Lispy)

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