Contents:
preface
- programming languages are aggregates of features
- features interact in ways that may not be easy to predict
- while we progress across features, also want to study variation between them
- mystery language approach: with a fixed syntax, explore the different ways the same feature can behave
- programming languages thought of as abstract syntax tree -> program that processes this tree is recursive function
evaluation
two types
- interpreter: consumes a program and simulates its execution.
- interpreter:: Program -> Value
- compiler: consumes a program and produces another program
- compiler:: Program_L -> Program_T
we have a choice:
eager
(f (+ 5 4))
(f 9)
or
lazy
(f (+ 5 4))
(+ 1) where x is replaced by (+ 5 4)
substitution
- is generally slow
representing programs
- our evaluator comsumes programs
- surface syntax: how to represent a program (human POV)
abstract syntax
- represent essence of the input, ignoring the superficial syntactic details
- in-computer representation of programs => AST, abstract syntax trees
- AST: tree-structured data that represent programs in programs
- by adopting a language’s primitives, we inherit its semantics