Metadata
- Author: Paul Graham
- URL: http://www.paulgraham.com/diff.html
- Read in: 2021
- Functional Programming
Notes
- Lisp embodied nine new ideas:
- Conditionals
- if-then-else construct
- While taken for granted today, they were invented by John McCarthy
- Fortran at that time had only conditional goto
- Function type
- Functions are first class objects in Lisp
- As a literal represantation, they can be stored in variables or passed as arguments
- Functions are first class objects in Lisp
- Recursion
- Lisp was the first language to support it
- This is implied by the previous point
- Lisp was the first language to support it
- Variables as pointers
- In Lisp, all variables are effectively pointers.
- Values are what have types, not variables
- Assigning or binding variables means copying pointers, not what they point to.
- Garbage-collection
- Programs composed of expressions
- Every expression returns a value
- A symbol type
- They differ from strings in that you can tesst equality by comparing a pointer
- The whole language always available
There is no real distinction between read-time, compile-time, and runtime. You can compile or run code while reading, read or run code while compiling, and read or compile code at runtime.
Running code at read-time lets users reprogram Lisp’s syntax; running code at compile-time is the basis of macros; compiling at runtime is the basis of Lisp’s use as an extension language in programs like Emacs; and reading at runtime enables programs to communicate using s-expressions, an idea recently reinvented as XML.
Lisp wasn’t designed to fix the mistakes in Fortran; it came about more as the byproduct of an attempt to axiomatize computation.
- Conditionals
