From f3e98ec134b50a121be3dcdc300a9f6df189f0c7 Mon Sep 17 00:00:00 2001
From: David Schmenk <dschmenk@sbcglobal.net>
Date: Wed, 2 Aug 2017 21:41:37 -0700
Subject: [PATCH] Add lambda functions
---
README.md | 35 ++++++++++++++++++++++++++++++++++-
1 file changed, 34 insertions(+), 1 deletion(-)
diff --git a/README.md b/README.md
index 5e00e31..c3ccd89 100755
--- a/README.md
+++ b/README.md
@@ -67,6 +67,7 @@ Different projects have led to the architecture of PLASMA, most notably Apple Pa
- [Assignment](#assignment)
- [Empty Assignments](#empty-assignments)
- [Increment and Decrement](#increment-and-decrement)
+ - [Lambda Function](#lambda_function)
- [Control Flow](#control-flow)
- [CALL](#call)
- [RETURN](#return)
@@ -464,6 +465,22 @@ keyin = @keyin2plus // address-of keyin2plus function
key = keyin()
```
+Lambda functions are anonymous functions that can be used to return a value (or multiple values). They can be used as function pointers to routines that need a quick and dirty expression. They are written an '&' (a poor man's lambda symbol) followed by parameters in parentheses, and the resultant expression. There are no local variables allowed.
+
+```
+word result
+
+def eval_op(x, y, op)
+ result = result + op(x, y)
+ return result
+end
+
+def keyin(x, y, key)
+ if key == '+'
+ eval(x, y, &(x, y) x + y)
+ fin
+end
+````
Control statements affect the flow of control through the program. There are conditional and looping constructs. The most widely used is probably the `if`/`elsif`/`else`/`fin` construct.
```
@@ -1004,7 +1021,6 @@ keypress = ^$C000 // read keyboard
^$C010 // read keyboard strobe, throw away value
```
-
### Increment and Decrement
PLASMA has an increment and decrement statement. This is different than the increment and decrement operations in languages like C and Java. Instead, they cannot be part of an expression and only exist as a statement in postfix:
@@ -1019,6 +1035,23 @@ i-- // decrement i by 1
puti(i) // print 4
```
+### Lambda Functions
+
+A Lambda function is a simple, anonymous function that can be passed to a function or assigned to a variable. It is called as a function pointer. The function can take a number of parameters and return a value based on the parameters and global values. By enclosing the expression of the lambda function in paranthesis, multiple values can be returned.
+
+```
+def lambdas#0
+ word lambda1
+ word lambda2
+ word x, y
+
+ lambda1 = &(a, b) a + b
+ lambda2 = &(a, b) (a + b, a - b)
+ x = lambda1(1, 2)#1
+ x, y = lambda2(3, 4)#2
+end
+````
+
### Control Flow
PLASMA implements most of the control flow that most high-level languages provide. It may do it in a slightly different way, though. One thing you won't find in PLASMA is GOTO - there are other ways around it.