Class 17: Higher-Order Procedures (2)

Held: Wednesday, 18 February 2004

Summary: Today we continue our investigations into higher-order procedures by grounding our discussion in further hands-on activities.

Related Pages:

• EBoard.
• Outline.
• First reading on higher-order procedures.
• Second reading on higher-order procedures.
• First lab on higher-order procedures.
• Second lab on higher-order procedures.

Due

• Exam 1.

Assignments:

• Homework 4: Higher-Order Vector Procedures.

Notes:

• There is no reading for tomorrow!
• Cool talk tomorrow at 4:30 on Biocomputing. Extra credit for attending and sending a reflective paragraph.

Overview:

• Operator sections.
• Rethinking procedure definitions.
• Questions on readings.
• Lab.

Operator Sections

• One thing programmers regularly observe is that they want to create new procedures by filling in one argument of another procedure.
• Procedures that build new procedures by filling in individual arguments are called operator sections.
• The simplest such procedure is left-section

  (define left-section
    (lambda (binproc left-param)
      (lambda (right-param)
        (binproc left-param right-param))))
  

Rethinking Procedure Definitions

• Once you've mastered higher-order procedures, your procedure definitions may begin to look quite different.
• For example, rather than writing

  (define symbol-or-string?
    (lambda (val)
      (or (symbol? val) (string? val))))
  

  You will write

  (define symbol-or-string? (conjunction symbol? string?))
  

• You will find that you also start to write procedures that return procedures.

Lab

• Are there any questions on the readings?
• Start the new lab.
• Reflect.