Lambda Expressions and Local Assignments


 

 

4.1 Lambda Expressions and Local Assignments

TBoS p.70-71, p.85-87

(λ x (* x x)) is written as '(/. X (* X X))' in Shen. It is customary to use capital letters for variables. '(/. X Y Z (+ X Y Z))' is an acceptable abbreviation for '(/. X (/. Y (/. Z (+ X Y Z))'. You can also write '(lambda X (+ X X))' though this form does not sustain abbreviations, '(lambda X Y (+ X Y))' is not legal (it should be '(lambda X (lambda Y (+ X Y)))').

Local assignments are made using 'let'. 'let' takes a variable v, an expression e11 and an expression e2 and binds v to the normal form of e1 in the evaluation of e2.

'let' is polyadic;

(let X1 a1 ... Xn an Y)

is short for

(let X1 a1 ... 
           (let Xn an) Y).
1. Introduction

2. License

3. History

4. The Core Language

4.1 Base Types
4.1.1 Symbols
4.1.2 Strings
4.1.3 Numbers
4.2 Function Applications
4.3 The Top Level
4.4 Arithmetic
4.5 Comments

4.6 Sequences

4.6.1 Lists
4.6.2 Tuples
4.6.3 Vectors

4.7 lambda and let
4.8 Global Assignments
4.9 Higher Order Functions
4.10 Lazy Evaluation
4.11 I/O
4.12 Loading Files
4.13 Streams
4.14 Exceptions
4.15 Hashing
4.16 Property Lists
4.17 Eval

5 Defining Functions

5.1 Partial Functions
5.2 List Handling Functions
5.3 String Handling Functions
5.4 Tuple Handling Functions
5.5 Vector Handling Functions
5.6 Guards
5.7 Backtracking
5.8 Writing in Kλ
5.9 Macros

6. Packages

7. Shen-YACC

7.1 Recognisor Generator
7.2 Semantic Actions

8. Shen Prolog

8.1 Sample Programs

9. Types

9.1 Types and Constructors
9.2 Functions and Types
9.3 Synonyms

10 Sequent Calculus

10.1 Recursive Types

10.2 Exotic Types

10.2.1 Dependent Types
10.2.2 Negative Types
10.2.3 Subtypes
10.2.4 The Type of All Sets

11 Glossary of Functions

12 The Syntax of Shen

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