Penlight

• Index

Contents

• Functions

Modules

• pl
• pl.Date
• pl.List
• pl.Map
• pl.MultiMap
• pl.OrderedMap
• pl.Set
• pl.app
• pl.array2d
• pl.class
• pl.comprehension
• pl.config
• pl.data
• pl.dir
• pl.file
• pl.func
• pl.input
• pl.lapp
• pl.lexer
• pl.luabalanced
• pl.operator
• pl.path
• pl.permute
• pl.pretty
• pl.seq
• pl.sip
• pl.strict
• pl.stringio
• pl.stringx
• pl.tablex
• pl.template
• pl.test
• pl.text
• pl.utils
• pl.xml

Topics

• 01-introduction.md
• 02-arrays.md
• 03-strings.md
• 04-paths.md
• 05-dates.md
• 06-data.md
• 07-functional.md
• 08-additional.md
• 09-discussion.md

Examples

• seesubst.lua
• sipscan.lua
• symbols.lua
• test-cmp.lua
• test-data.lua
• test-listcallbacks.lua
• test-pretty.lua
• test-symbols.lua
• testapp.lua
• testclone.lua
• testconfig.lua
• testglobal.lua
• testinputfields.lua
• testinputfields2.lua
• testxml.lua
• which.lua

Module pl.func

Functional helpers like composition, binding and placeholder expressions.

Placeholder expressions are useful for short anonymous functions, and were inspired by the Boost Lambda library.

> utils.import 'pl.func'
> ls = List{10,20,30}
> = ls:map(_1+1)
{11,21,31}

They can also be used to bind particular arguments of a function.

> p = bind(print,'start>',_0)
> p(10,20,30)
> start>   10   20  30

See the Guide

Dependencies: pl.utils , pl.tablex

Functions

import (tname, context)	wrap a table of functions.
register (fun, name)	register a function for use in placeholder expressions.
tail (ls)	all elements of a table except the first.
repr (e, lastpred)	create a string representation of a placeholder expression.
instantiate (e)	instantiate a PE into an actual function.
I (e)	instantiate a PE unless it has already been done.
curry (fn, p)	bind the first parameter of the function to a value.
compose (f, g)	create a function which chains two functions.
bind (fn, ...)	bind the arguments of a function to given values.

Functions

import (tname, context)

wrap a table of functions. This makes them available for use in placeholder expressions.

Parameters:

• tname: a table name
• context: context to put results, defaults to environment of caller

register (fun, name)

register a function for use in placeholder expressions.

Parameters:

• fun: a function
• name: an optional name

Returns:

a placeholder functiond

tail (ls)

all elements of a table except the first.

Parameters:

• ls: a list-like table.

repr (e, lastpred)

create a string representation of a placeholder expression.

Parameters:

• e: a placeholder expression
• lastpred: not used

instantiate (e)

instantiate a PE into an actual function. First we find the largest placeholder used, e.g. _2; from this a list of the formal parameters can be build. Then we collect and replace any non-PE values from the PE, and build up a constant binding list. Finally, the expression can be compiled, and e.__PE_function is set.

Parameters:

• e: a placeholder expression

Returns:

a function

I (e)

instantiate a PE unless it has already been done.

Parameters:

• e: a placeholder expression

Returns:

the function

curry (fn, p)

bind the first parameter of the function to a value.

Parameters:

• fn: a function of one or more arguments
• p: a value

Usage:

(curry(math.max,10))(20) == math.max(10,20)

Returns:

a function of one less argument

compose (f, g)

create a function which chains two functions.

Parameters:

• f: a function of at least one argument
• g: a function of at least one argument

Usage:

printf = compose(io.write,string.format)

Returns:

a function

bind (fn, ...)

bind the arguments of a function to given values. bind(fn,v,_2) is equivalent to curry(fn,v).

Parameters:

• fn: a function of at least one argument
• ...: values or placeholder variables

Usage:

• (bind(f,_1,a))(b) == f(a,b)

• (bind(f,_2,_1))(a,b) == f(b,a)

Returns:

a function